Electrolyte for rechargeable electrochemical cell

ABSTRACT

The present invention provides an aqueous electrolyte for use in rechargeable zinc-halide storage batteries that possesses improved stability and durability and improves zinc-halide battery performance. One aspect of the present invention provides an electrolyte for use in a secondary zinc bromine electrochemical cell comprising from about 30 wt % to about 40 wt % of ZnBr 2  by weight of the electrolyte; from about 5 wt % to about 15 wt % of KBr; from about 5 wt % to about 15 wt % of KCl; and one or more quaternary ammonium agents, wherein the electrolyte comprises from about 0.5 wt % to about 10 wt % of the one or more quaternary ammonium agents.

CROSS REFERENCE TO RELATED APPLICATION

This PCT application claims the benefit of U.S. provisional applicationNos. 62/060,273, filed on Oct. 6, 2014; 62/170,200, filed on Jun. 3,2015; and 62/173,415, filed on Jun. 10, 2015. Each of these documents isincorporated herein by reference in its entirety.

TECHNICAL FIELD

This invention relates to electrolytes that are useful in zinc haliderechargeable electrochemical cells (e.g., storage batteries). Morespecifically, this invention relates to aqueous electrolytes thatreversibly electrolyze zinc halide in electrochemical storage cells orbatteries.

BACKGROUND

Zinc-halide batteries were developed as devices for storing electricalenergy. Traditional zinc-halide batteries (e.g., zinc-bromine batteries)employed bipolar electrodes disposed in a static, i.e., non-flowing,zinc-bromide aqueous solution. The process of charging and dischargingelectrical current in a zinc-halide battery is generally achievedthrough a reaction of redox couples like Zn²⁺/Zn(s) and X⁻/X₂ in zinchalide electrolyte, where X is a halogen (e.g., Cl, Br, or I).

When the battery is charged with electrical current, the followingchemical reactions occur:

Zn²⁺+2e ⁻→Zn

2X⁻→X₂+2e ⁻.

Conversely, when the battery discharges electrical current, thefollowing chemical reactions occur:

Zn→Zn²⁺+2e ⁻

X₂+2e ⁻→2X⁻.

Additionally, in some batteries, polyhalide reactions may also occur.Some of these examples are described by the following:

X₃ ⁻+2e ⁻→3X⁻ or

X_(n) ⁻ +ne ⁻ →nX⁻ for n≧3.

The polyhalide reactions pictured above can include reactions betweenlike halogens, e.g. Br₃, and reactions between non-like halogens, e.g.,mixed halogens such as Br₂Cl.

These zinc-halide storage batteries were typically configured in abipolar electrochemical cell stack, wherein each electrode is disposedin an aqueous zinc salt electrolyte. However, the performance of thesestorage batteries was highly inefficient due to secondary reactions ofthe dissolved species in the aqueous electrolyte. For example, insolution, elemental bromine exists in equilibrium with bromide ions toform polybromide ions, Br_(m) ⁻, where m=3, 5, or 7. Elemental brominealso possesses an increased vapor pressure that promotes hazardouspressure in the batteries. Furthermore, when aqueous zinc halide saltsare ionized, zinc ions can exist as various complex ions and ion pairs,which promotes zinc dendrite formation and increased incidence ofself-discharge in the batteries. To improve electrolyte durability inthe batteries, halogen sequestration agents were added (e.g., quaternaryammonium salts); however, these sequestration agents possessed reducedsolubility and reduce the stability of the electrolyte over numerouscharge cycles.

SUMMARY OF THE INVENTION

The present invention provides an aqueous electrolyte for use inrechargeable zinc-halide storage batteries that possesses improvedstability and durability and improves zinc-halide battery performance.In one aspect, the electrolyte comprises from about 25 wt % to about 70wt % of ZnBr₂; from about 5 wt % to about 50 wt % of water; and one ormore quaternary ammonium agents, wherein the electrolyte comprises fromabout 0.05 wt % to about 10 wt % of the one or more quaternary ammoniumagents.

In some embodiments, the electrolyte further comprises from about 1 wt %to about 15 wt % of KBr; and from about 5 wt % to about 20 wt % of KCl.

In some embodiments, the electrolyte comprises from about 27 wt % toabout 40 wt % of ZnBr₂. For example, the electrolyte comprises fromabout 28 wt % to about 37 wt % of ZnBr₂.

In some embodiments, the electrolyte comprises from about 1.5 wt % toabout 7.5 wt % of ZnCl₂.

And, in some embodiments, the electrolyte comprises from about 30 wt %to about 45 wt % of water. For example, the electrolyte comprises fromabout 35 wt % to about 41 wt % of water.

In alternative embodiments, the electrolyte comprises from about 2 wt %to about 10 wt % of KBr. For example, the electrolyte comprises fromabout 7.3 wt % to about 9.2 wt % of KBr.

And, in some embodiments, the electrolyte comprises from about 7 wt % toabout 17 wt % of KCl.

In some embodiments, the electrolyte comprises from about 0.5 wt % toabout 10 wt % of a glyme. And, in some embodiments, the glyme comprisesmonoglyme, diglyme, triglyme, tetraglyme, pentaglyme, hexaglyme, or anycombination thereof. For instance, the electrolyte comprises from about2 wt % to about 4 wt % of tetraglyme.

In some embodiments, the electrolyte comprises from about 0.5 wt % toabout 2.5 wt % of an ether selected from DME-PEG, dimethyl ether, or anycombination thereof. For example, the electrolyte comprises DME-PEG, andthe DME-PEG has an average molecular weight of from about 350 amu toabout 3000 amu. In other examples, the DME-PEG has an average molecularweight of from about 1200 amu to about 3000 amu. And, in someembodiments, the DME-PEG is DME-PEG 2000, DME-PEG 1000, or a combinationthereof. In other instances, the electrolyte comprises from about 1 wt %to about 2 wt % DME-PEG 2000. And, in some instances, the electrolytecomprises from about 0.25 wt % to about 0.75 wt % DME-PEG 1000. Forexample, the electrolyte comprises from about 1 wt % to about 2 wt %DME-PEG 2000 and from about 0.25 wt % to about 0.75 wt % DME-PEG 1000.

In some embodiments, the electrolyte further comprises from about 0.1 wt% to about 1.0 wt % of an alcohol, wherein the alcohol is substantiallymiscible in water. For example, the alcohol comprises a C₁₋₄ alcohol. Inother examples, the alcohol comprises methanol, ethanol, 1-propanol,iso-propanol, 1-butanol, sec-butanol, iso-butanol, tert-butanol, or anycombination thereof. For instance, the electrolyte comprises from about0.25 wt % to about 0.75 wt % of tert-butanol.

In some embodiments, the electrolyte comprises from about 0.5 wt % toabout 5 wt % of a C₁₋₁₀ glycol. In some examples, the glycol comprisesethylene glycol, propylene glycol, 1,3-butylene glycol, 1,4-butyleneglycol, neopentyl glycol, hexalene glycol, or any combination thereof.And, in some embodiments, the electrolyte comprises from about 0.25 wt %to about 2.5 wt % of neopentyl glycol.

In some embodiments, the electrolyte further comprising from about 0.05wt % to about 20 wt % of one or more quaternary ammonium agents. And, insome examples, the one or more quaternary ammonium agents comprises aquaternary ammonium agent selected from the group consisting of ammoniumchloride, tetraethylammonium bromide, trimethylpropylammonium bromide,N-methyl-N-ethylmorpholinium bromide, N-methyl-N-ethylmorpholiniumbromide (MEMBr), 1-ethyl-1-methylmorpholinium bromide,N-methyl-N-butylmorpholinium bromide, N-methyl-N-ethylpyrrolidiniumbromide, N,N,N-triethyl-N-propylammonium bromide,N-ethyl-N-propylpyrrolidinium bromide, N-propyl-N-butylpyrrolidiniumbromide, N-methyl-N-butylpyrrolidinium bromide,1-methyl-1-butylpyrrolidinium bromide,N-ethyl-N-(2-chloroethyl)pyrrolidinium bromide,N-methyl-N-hexylpyrrolidinium bromide, N-methyl-N-pentylpyrrolidiniumbromide, N-ethyl-N-pentylpyrrolidinium bromide,N-ethyl-N-butylpyrrolidinium bromide,trimethylene-bis(N-methylpyrrolidinium) dibromide,N-butyl-N-pentylpyrrolidinium bromide, N-methyl-N-propylpyrrolidiniumbromide, N-propyl-N-pentylpyrrolidinium bromide,1-ethyl-4-methylpyridinium bromide, 1-ethyl-2-methylpyridinium bromide,1-butyl-3-methylpyridinium bromide, cetyltrimethylammonium bromide, andany combination thereof. In some examples, quaternary ammonium agentsincludes at least one of 1-ethyl-4-methylpyridinium bromide or1-ethyl-2-methylpyridinium bromide. In some instances, the one or morequaternary ammonium agents comprises a quaternary ammonium agentselected from the group consisting of ammonium chloride,tetraethylammonium bromide, trimethylpropylammonium bromide,N-methyl-N-ethylmorpholinium bromide (MEMBr),1-ethyl-1-methylmorpholinium bromide, N-methyl-N-ethylpyrrolidiniumbromide, 1-methyl-1-butylpyrrolidinium bromide,1-ethyl-4-methylpyridinium bromide, 1-ethyl-2-methylpyridinium bromide,1-butyl-3-methylpyridinium bromide, cetyltrimethylammonium bromide, andany combination thereof.

In some embodiments, the one or more quaternary ammonium agentscomprises about 3.5 wt % to about 4.5 wt % of 1-ethyl-4-methylpyridiniumbromide by weight of the electrolyte. In some embodiments, the one ormore quaternary ammonium agents comprises about 1 wt % to about 7 wt %of 1-ethyl-2-methylpyridinium bromide by weight of the electrolyte. Insome embodiments, the one or more quaternary ammonium agents comprisesabout 1.5 wt % to about 2.5 wt % of 1-methyl-1-butylpyrrolidiniumbromide by weight of the electrolyte. In some embodiments, the one ormore quaternary ammonium agents comprises about 1.5 wt % to about 2.5 wt% of 1-butyl-3-methylpyridinium bromide by weight of the electrolyte. Insome embodiments, the one or more quaternary ammonium agents comprisesabout 1.5 wt % to about 5 wt % of 1-methyl-1-ethylmorpholinium bromideby weight of the electrolyte. In some embodiments, the one or morequaternary ammonium agents comprises about 0.5 wt % to about 1.5 wt % ofN-methyl-N-ethylmorpholinium bromide (MEMBr) by weight of theelectrolyte. In some embodiments, the one or more quaternary ammoniumagents comprises about 14.5 wt % to about 16.5 wt % ofN-methyl-N-ethylpyrrolidinium bromide by weight of the electrolyte. Insome embodiments, the one or more quaternary ammonium agents comprisesabout 2 wt % to about 3 wt % of trimethylpropylammonium bromide byweight of the electrolyte. In some embodiments, the one or morequaternary ammonium agents comprises about 2 wt % to about 8 wt %tetraethylammonium bromide by weight of the electrolyte. In someembodiments, the one or more quaternary ammonium agents comprises about0.05 wt % to about 0.2 wt % of cetyltrimethylammonium bromide by weightof the electrolyte.

And, in other embodiments, the electrolyte comprising less than 1 wt %of one or more additives selected from Sn, In, Ga, Al, Tl, Bi, Pb, Sb,Ag, Mn, or Fe by weight of the electrolyte. For example, the one or moreadditives are selected from about 0.0008 wt % to about 0.0012 wt % ofSnCl₂.H₂O, from about 0.0008 wt % to about 0.0012 wt % of In, andcombinations thereof.

In some embodiments, the electrolyte comprising an acid, or theconjugate base of an acid, selected from acetic acid, nitric acid, andcitric acid. For example, the electrolyte comprises from about 0.3 wt %to about 0.6 wt % acetic acid by weight of the electrolyte. In anotherexample, the electrolyte comprises from about 0.12 wt % to about 0.08 wt% nitric acid by weight of the electrolyte. And, in some examples, theelectrolyte comprises from about 3.5 wt % to about 4.5 wt % citric acidby weight of the electrolyte. In alternative examples, the electrolytecomprises from about 3.5 wt % to about 4.5 wt % potassium dihydrogencitrate by weight of the electrolyte.

In other embodiments, the electrolyte comprises from about 0.05 wt % toabout 0.75 wt % of a crown ether (e.g., 18 crown 6, 15 crown 5, or anycombination thereof) by weight of the electrolyte. In some instances,the electrolyte comprises from about 0.15 wt % to about 0.5 wt % of18-crown-6 by weight of the electrolyte. In other instances, theelectrolyte comprises from about 0.05 wt % to about 0.2 wt % of15-crown-5 by weight of the electrolyte.

Another aspect of the present invention provides an electrolyte for usein a secondary zinc halide electrochemical cell comprising from about 27wt % to about 40 wt % of ZnBr₂ by weight of the electrolyte; from about35 wt % to about 41 wt % of water; from about 7.3 wt % to about 9.2 wt %of KBr; from about 7 wt % to about 17 wt % of KCl; from about 0.3 wt %to about 0.6 wt % acetic acid; and from about 2 wt % to about 8 wt %tetraethylammonium bromide, wherein these weight percents are by weightof the electrolyte.

Another aspect of the present invention provides an electrolyte for usein a secondary zinc halide electrochemical cell comprising from about 27wt % to about 40 wt % of ZnBr₂ by weight of the electrolyte; and fromabout 1 wt % to about 10 wt % of 1-ethyl-4-methylpyridinium bromide orabout 1 wt % to about 7 wt % of 1-ethyl-2-methylpyridinium bromide.

Another aspect of the present invention provides an electrolyte for usein a secondary zinc halide electrochemical cell comprising from about 27wt % to about 40 wt % of ZnBr₂ by weight of the electrolyte; and from 5ppm to about 15 ppm of In, Sn, or both. In some embodiments, theelectrolyte further comprises 1-ethyl-4-methylpyridinium bromide.

In some embodiments, the electrolyte further comprises from about 0.05wt % to about 0.2 wt % of cetyltriethylammonium bromide (CTAB) by weightof the electrolyte.

In some embodiments, the electrolyte comprises from about 3.5 wt % toabout 4.5 wt % of citric acid monohydrate by weight of the electrolyte.

In some embodiments, the electrolyte comprises from about 3.5 wt % toabout 4.5 wt % of potassium dihydrogen citrate monohydrate by weight ofthe electrolyte.

Another aspect of the present invention provides an electrolyte for usein a secondary zinc halide electrochemical cell comprising from about 27wt % to about 40 wt % of ZnBr₂ by weight of the electrolyte; from about35 wt % to about 41 wt % of water from about 7.3 wt % to about 9.2 wt %of KBr; from about 7 wt % to about 17 wt % of KCl; from about 0.15 wt %to about 0.5 wt % of 18-crown-6; and from about 0.05 wt % to about 0.2wt % of cetyltrimethylammonium bromide, wherein the weight percents areby weight of the electrolyte.

In some embodiments, the electrolyte comprises from about 2 wt % toabout 8 wt % tetraethylammonium bromide by weight of the electrolyte.

In some embodiments, the electrolyte comprises from about 0.3 wt % toabout 0.6 wt % acetic acid by weight of the electrolyte.

In some embodiments, the electrolyte comprises from about 1 wt % toabout 2 wt % DME-PEG 2000. In some embodiments, the electrolytecomprises from about 0.25 wt % to about 0.75 wt % DME-PEG 1000. In otherembodiments, the electrolyte comprises from about 1 wt % to about 2 wt %DME-PEG 2000 and from about 0.25 wt % to about 0.75 wt % DME-PEG 1000.

Another aspect of the present invention provides a method of preparingan electrolyte for use in a secondary zinc halide electrochemical cellcomprising mixing ZnBr₂, KBr, KCl, and one or more quaternary ammoniumagents under aqueous conditions to generate a mixture and stirring themixture until the solids have dissolved or are homogenously distributedthroughout the mixture, wherein the mixture comprises from about 27 wt %to about 40 wt % of ZnBr₂; from about 7.3 wt % to about 9.2 wt % of KBr;from about 7 wt % to about 17 wt % of KCl; from about 0.05 wt % to about20 wt % of the one or more quaternary ammonium agents; and from about 35wt % to about 41 wt % of water.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings.

FIG. 1 shows an exploded view of an electrochemical cell according to anembodiment of the present invention.

FIGS. 2A and 2B are front and side views, respectively, of a bipolarelectrode according to an embodiment of the present invention.

FIG. 3 shows an exploded view of a bipolar electrode according to anembodiment of the present invention.

FIG. 4A shows a front view of a bipolar electrode according to anembodiment of the present invention.

FIG. 4B shows an exploded view of a bipolar electrode according to anembodiment of the present invention.

FIG. 5 shows a view of the back surface of an electrode plate having asandblasted area according to an embodiment of the present invention.

FIGS. 6A and 6B show a front and side view, respectively, of a cathodecage according to an embodiment of the present invention.

FIGS. 7A and 7B show a front view of a cathode cage and a magnified viewof a cathode cage material having holes therethrough, respectively,according to an embodiment of the present invention.

FIG. 8 shows a cross-sectional view of a portion of an electrochemicalcell including an interface between a front surface of a bipolarelectrode plate (including the cathode assembly mounted thereon) and theback surface of a second electrode plate or an inner surface of aterminal endplate according to an embodiment of the present invention.

FIG. 9 shows a front, side, and top perspective view of a carbonmaterial for use as a cathode according to an embodiment of the presentinvention.

FIG. 10 illustrates experimental data of spacing between thethree-dimensional shape profiles of a bipolar electrode plate andcathode cage with respect to the Z-axis and X-axis according to anembodiment of the present invention.

FIG. 11 illustrates experimental data of spacing between thethree-dimensional shape profiles of a bipolar electrode plate andcathode with respect to the Z-axis and the Y-axis according to anembodiment of the present invention.

FIG. 12 shows a perspective view of a terminal assembly according to anembodiment of the present invention.

FIG. 13 shows a top perspective view of a terminal assembly for abipolar battery comprising a terminal endplate and a conductivecup-shaped member having a substantially elliptical rim joined to theendplate according to an embodiment of the present invention.

FIG. 14 shows a top view of the endplate of the terminal assembly ofFIG. 13 having an electrochemically active region comprising a firstsurface area enclosed by the rim of the conductive cup-shaped member anda remaining second surface defined by an outer periphery of the rim andperipheral edges of the electrochemically active region according to anembodiment of the present invention.

FIG. 15 is a cross-sectional view taken along line 17-17 of FIG. 13showing the conductive cup-shaped member and a remaining second surfacedefined by an outer periphery of the rim and peripheral edges of theelectrochemically active region according to an embodiment of thepresent invention.

FIG. 16 is a top perspective view of the terminal assembly of FIG. 13showing the bipolar endplate and the conductive-cup shaped membercomprising a substantially circular rim according to an embodiment ofthe present invention.

FIG. 17 is a cross-sectional view taken along line 15-15 of FIG. 13showing the terminal assembly further comprising a frame member opposedto and receiving a second surface of the terminal endplate on a sideopposite the conductive cup-shaped member according to an embodiment ofthe present invention.

FIG. 18 is a side view of a battery stack comprising a cathode terminaland an anode terminal with bipolar electrodes and frame members betweencompression plates according to an embodiment of the present invention.

FIG. 19 is a top perspective view of a battery stack comprising a pairof terminal assemblies at corresponding proximal and distal ends of thebattery module according to an embodiment of the present invention.

FIG. 20 is an exploded view of the battery stack of FIG. 18 according toan embodiment of the present invention.

FIG. 21 shows a front view of a seal for use in the battery module ofFIG. 20 and a cross sectional view of the seal.

FIG. 22 shows a top perspective view of compression plates for thecathode terminal and anode terminal of the battery stack of FIG. 18according to an embodiment of the present invention.

FIG. 23 shows a front view and side view of a frame for use in thebattery stack of FIG. 18 according to an embodiment of the presentinvention.

FIG. 24 shows representative behavior of a battery stack according to anembodiment of the present invention in terms of discharge energy overseveral charge cycles.

FIGS. 25A and 25B show representative behavior of a battery moduleaccording to an embodiment of the present invention. FIG. 25A shows theruntime vs. the average discharge power of the battery. FIG. 25B showsenergy efficiency vs. average discharge power of the battery.

FIG. 26 shows representative behavior of a battery module according toan embodiment of the present invention in terms of discharge energy vs.average discharge power.

FIGS. 27A and 27B show representative behavior of a battery moduleaccording to an embodiment of the present invention. FIG. 27A showsenergy efficiency of the battery over several charge cycles. FIG. 27Bshows discharge runtime of the battery over several charge cycles.

FIG. 28 shows representative behavior of an electrolyte according to anembodiment of the present invention in terms of plots of energy as afunction of charge cycle in test cells employing an electrolyte of thepresent invention and electrolytes reported in the published literature.

FIG. 29A shows representative behavior of an electrolyte according to anembodiment of the present invention in terms of capacity as a functionof charge cycle in test cells employing an electrolyte of the presentinvention and electrolytes reported in the published literature.

FIG. 29B shows representative behavior of an electrolyte according to anembodiment of the present invention in terms of electric potential as afunction of charge cycle in test cells employing an electrolyte of thepresent invention and electrolytes reported in the published literature.

FIGS. 30A and 30B are photographs of zinc metal plated on the backsurfaces of electrode plates, wherein the corresponding cathode cageshave an un-modulated pattern of holes.

FIGS. 31A, 31B and 31C are photographs of zinc metal plated on the backsurfaces of the electrode plates, wherein the corresponding cathodecages have a modulated pattern of holes.

FIG. 32 shows representative behavior of various bromine complexingagents in terms of power (max. power at limiting current for Br₂reduction) as a function of stability (change in pH at 60° C. after 7days).

FIG. 33 shows a comparison of bromine activity of various ethyl methylpyridiniums in terms of logarithmic current as a function of voltage.

FIG. 34 shows a comparison of different polyethers as bromine complexingagents in terms of power (max. power at limiting current for Br₂reduction) as a function of stability (change in pH at 60° C. after 7days).

FIG. 35 is a plot of discharge capacity (mAh) vs. charge cycle no. forelectrochemical cells of the present invention assembled to includeelectrolyte formulations from Example No. 1.

FIG. 36 is a plot of Coulombic Efficiency (%) vs. charge cycle no. forelectrochemical cells of the present invention assembled to includeelectrolyte formulations from Example No. 1.

FIG. 37 is a plot of Run Time (hrs) vs. charge cycle no. forelectrochemical cells of the present invention assembled to includeelectrolyte formulations from Example No. 1.

FIG. 38 is a plot of Energy Efficiency (%) vs. charge cycle no. forelectrochemical cells of the present invention assembled to includeelectrolyte formulations from Example No. 1.

FIG. 39 are plots of cyclic voltammetry measurements for battery stacksof the present invention assembled to include electrolyte formulationsfrom Example No. 5.

The figures are provided by way of example and are not intended to limitthe scope of the invention.

DETAILED DESCRIPTION

The present invention provides an electrolyte for use in secondary,i.e., rechargeable, zinc halide storage batteries (e.g., bipolar flow ornon-flow batteries).

I. Definitions

As used herein, the term “electrochemical cell” or “cell” are usedinterchangeably to refer to a device capable of either generatingelectrical energy from chemical reactions or facilitating chemicalreactions through the introduction of electrical energy.

As used herein, the term “battery” encompasses electrical storagedevices comprising at least one electrochemical cell. A “secondarybattery” is rechargeable, whereas a “primary battery” is notrechargeable. For secondary batteries of the present invention, abattery anode is designated as the positive electrode during discharge,and as the negative electrode during charge.

As used herein, an “electrolyte” refers to a substance that behaves asan electrically conductive medium. For example, the electrolytefacilitates the mobilization of electrons and cations in the cell.Electrolytes include mixtures of materials such as aqueous solutions ofmetal halide salts (e.g., ZnBr₂, ZnCl₂, or the like).

As used herein, the term “electrode” refers to an electrical conductorused to make contact with a nonmetallic part of a circuit (e.g., asemiconductor, an electrolyte, or a vacuum). An electrode may also referto either an anode or a cathode.

As used herein in, the term “anode” refers to the negative electrodefrom which electrons flow during the discharging phase in the battery.The anode is also the electrode that undergoes chemical oxidation duringthe discharging phase. However, in secondary, or rechargeable, cells,the anode is the electrode that undergoes chemical reduction during thecell's charging phase. Anodes are formed from electrically conductive orsemiconductive materials, e.g., metals (e.g., titanium or TiC coatedtitanium), metal oxides, metal alloys, metal composites, semiconductors,or the like.

As used herein, the term “cathode” refers to the positive electrode intowhich electrons flow during the discharging phase in the battery. Thecathode is also the electrode that undergoes chemical reduction duringthe discharging phase. However, in secondary or rechargeable cells, thecathode is the electrode that undergoes chemical oxidation during thecell's charging phase. Cathodes are formed from electrically conductiveor semiconductive materials, e.g., metals, metal oxides, metal alloys,metal composites, semiconductors, or the like.

As used herein, the term “bipolar electrode” refers to an electrode thatfunctions as the anode of one cell and the cathode of another cell. Forexample, in a battery stack, a bipolar electrode functions as an anodein one cell and functions as a cathode in an immediately adjacent cell.In some examples, a bipolar electrode comprises two surfaces, a cathodesurface and an anode surface, wherein the two surfaces are connected bya conductive material. For instance, a bipolar electrode plate may haveopposing surfaces wherein one surface is the anode surface, the othersurface is the cathode surface, and the conductive material is thethickness of the plate between the opposing surfaces.

As used herein, the term “halide” refers to a binary compound of ahalogen with another element or radical that is less electronegative (ormore electropositive) than the halogen, to make a fluoride, chloride,bromide, iodide, or astatide compound.

As used herein, the term “halogen” refers to any of the elementsfluorine, chlorine, bromine, iodine, and astatine, occupying group VIIA(17) of the periodic table. Halogens are reactive nonmetallic elementsthat form strongly acidic compounds with hydrogen, from which simplesalts can be made.

As used herein, the term “anion” refers to any chemical entity havingone or more permanent negative charges. Examples of anions include, butare not limited to fluoride, chloride, bromide, iodide, arsenate,phosphate, arsenite, hydrogen phosphate, dihydrogen phosphate, sulfate,nitrate, hydrogen sulfate, nitrite, thiosulfate, sulfite, perchlorate,iodate, chlorate, bromate, chlorite, hypochlorite, hypobromite,carbonate, chromate, hydrogen carbonate (bicarbonate), dichromate,acetate, formate, cyanide, amide, cyanate, peroxide, thiocyanate,oxalate, hydroxide, and permanganate.

As used herein, “glyme” refers to an ether (e.g., a glycol ether).Examples include, but are not limited to, monoglyme (i.e.,1,2-dimethoxyethane), diglyme (i.e., bis(2-methoxyethyl) ether,tetraglyme (i.e., tetraethylene glycol dimethyl ether), pentaglyme,hexaglyme, heptaglyme, or any combination thereof.

As used herein, a “titanium material” may include, but is not limitedto, titanium (in any oxidation state), TiC, alloys of TiC such asTiC_(x)M (where x is 0, 1, 2, 3, or 4 and M is a metal), titaniumcarbohyrides, non-stoichiometric titanium-carbon compounds, andcombinations thereof.

As used herein, “titanium carbide” is used interchangeably with“titanium carbide material” and includes, but is not limited to TiC,alloys of TiC such as TiC_(x)M (where x is 0, 1, 2, 3, or 4 and M is ametal), titanium carbohyrides, non-stoichiometric titanium-carboncompounds, and combinations thereof.

As used herein, the term “zinc metal” refers to elemental zinc, alsocommonly known as Zn(0) or Zn⁰.

As used herein, the term “dimethyl ether poly(ethylene glycol)” and itsabbreviation “DME-PEG” are used interchangeably to refer to a polymerhaving the structure

where n is an integer. DME-PEG 1000 refers to a DME-PEG polymer having anumber average molecular weight (M_(n)) about 1000, and DME-PEG 2000refers to a DME-PEG polymer having a number average molecular weight(M_(n)) of about 2000.

As used herein, the term “dimethyl ether” refers to an organic compoundhaving the formula CH₃OCH₃.

As used herein, the term “alcohol” refers to any organic compound whosemolecule contains one or more hydroxyl groups attached to a carbon atom.Examples of alcohols include methanol, ethanol, 1-propanol (i.e.,n-propanol), 2-propanol (i.e., iso-propanol), 1-butanol (i.e.,n-butanol), sec-butanol, iso-butanol, tert-butanol, 1-pentanol, or anycombination thereof.

As used herein, the term “hydroxyl group” refers to an —OH group.

As used herein, the term “glycol” refers to any of a class of organiccompounds belonging to the alcohol family. In the molecule of a glycol,two hydroxyl (—OH) groups are attached to different carbon atoms.Examples of glycols include C₁₋₁₀ glycols including ethylene glycol,propylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, neopentylglycol, hexalene glycol, or any combination thereof. Other examples ofglycols include substituted ethylene and substituted propylene clycols.

As used herein, the term “weight percent” and its abbreviation “wt %”are used interchangeably to refer to the product of 100 times thequotient of mass of one or more components divided by total mass of amixture or product containing said component:

wt %=100%×(mass of component(s)/total mass)

When referring to the concentration of components or ingredients forelectrolytes, as described herein, wt % is based on the total weight ofthe electrolyte.

As used herein, the term “quaternary ammonium agent” refers to anycompound, salt, or material comprising a quaternary nitrogen atom. Forexample, quaternary ammonium agents include ammonium halides (e.g.,NH₄Br, NH₄Cl, or any combination thereof), tetra-alkylammonium halides(e.g., tetramethylammonium bromide, tetramethylammonium chloride,tetraethylammonium bromide, tetraethylammonium chloride, combinationsthereof or the like), heterocyclic ammonium halides (e.g.,N-methyl-N-ethylpyrrolidinium halide, N-ethyl-N-methylpyrrolidiniumhalide, combinations thereof, or the like), or any combination thereof.Tetra-alkylammonium halides may be symmetrically substituted orasymmetrically substituted with respect to the substituents of thequaternary nitrogen atom.

As used herein, the term “ammonium bromide complexing agent” refers toany compound, salt, or material comprising a quaternary nitrogen atom,wherein the quaternary nitrogen atom is not part of an imidazolium,pyridinium, pyrrolidinium, morpholinium, or phosphonium moiety. Examplesof ammonium bromide complexing agents include: tetraethylammoniumbromide, trimethylpropylammonium bromide, dodecyltrimethylammoniumbromide, cetyltriethylammonium bromide, and hexyltrimethylammoniumbromide.

As used herein, the term “imidazolium bromide complexing agent” refersto any compound, salt, or material comprising a quaternary nitrogenatom, wherein the quaternary nitrogen atom is part of an imidazoliummoiety. Examples of imidazolium bromide complexing agents include:1-ethyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazoliiumbromide, 1-ethyl-2,3-dimethylimidazolium bromide,1-decyl-3-methylimidazolium bromide, 1-butyl-2,3-dimethylimidazoliumbromide, 1-methyl-3-octylimidazollium bromide, and1-methyl-3-hexylimidazolium bromide.

As used herein, the term “pyridinium bromide complexing agent” refers toany compound, salt, or material comprising a quaternary nitrogen atom,wherein the quaternary nitrogen atom is part of a pyridinium moiety.Examples of pyridinium bromide complexing agents include:1-ethyl-3-methylpyridinium bromide, 1-ethyl-2-methylpyridinium bromide,1-butyl-3-methylpyridinium bromide, 1-butyl-3-methylpyridinium bromide,1-butyl-4-methylpyridinium bromide, and 1-hexylpyridinium bromide.

As used herein, the term “pyrrolidinium bromide complexing agent” refersto any compound, salt, or material comprising a quaternary nitrogenatom, wherein the quaternary nitrogen atom is part of a pyrrolidiniummoiety. An example of a pyrrolidinium bromide complexing agent is1-butyl-1-methylpyrrolidinium bromide.

As used herein, the term “morpholinium bromide complexing agent” refersto any compound, salt, or material comprising a quaternary nitrogenatom, wherein the quaternary nitrogen atom is part of a morpholiniummoiety. An example of a morpholinium bromide complexing agent isN-ethyl-N-methylmorpholinium bromide.

As used herein, the term “phosphonium bromide complexing agent” refersto any compound, salt, or material comprising a quaternary phosphoniumatom. An example of a phosphonium bromide complexing agent istetraethylphosphonium bromide.

As used herein, the term “crown ether” refers to a cyclic chemicalcompound consisting of a ring containing at least three ether groups.Examples of crown ethers include 12-crown-4, 15-crown-5, 18-crown-6,dibenzo-18-crown-6, and diaza-18-crown-6.

As used herein, an “alkyl” group refers to a saturated aliphatichydrocarbon group containing 1-20 (e.g., 1-16, 1-12, 1-8, 1-6, or 1-4)carbon atoms. An alkyl group can be straight or branched. Examples ofalkyl groups include, but are not limited to, methyl, ethyl, propyl,isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl,heptyl, 2-ethylhexyl, octyl, nonyl, decyl, dodecyl, and cetyl.

As used herein, an “aryl” group used alone or as part of a larger moietyas in “aralkyl”, “aralkoxy”, or “aryloxyalkyl” refers to monocyclic(e.g., phenyl); bicyclic (e.g., indenyl, naphthalenyl,tetrahydronaphthyl, tetrahydroindenyl); tricyclic (e.g., fluorenyl,tetrahydrofluorenyl, anthracenyl, or tetrahydroanthracenyl); or abenzofused group having 3 rings. For example, a benzofused groupincludes phenyl fused with two or more C₄₋₈ carbocyclic moieties. Anaryl is optionally substituted with one or more substituents includingaliphatic (e.g., alkyl, alkenyl, or alkynyl); cycloalkyl;(cycloalkyl)alkyl; heterocycloalkyl; (heterocycloalkyl)alkyl; aryl;heteroaryl; alkoxy; cycloalkyloxy; heterocycloalkyloxy; aryloxy;heteroaryloxy; aralkyloxy; heteroaralkyloxy; aroyl; heteroaroyl; amino;aminoalkyl; nitro; carboxy; carbonyl (e.g., alkoxycarbonyl,alkylcarbonyl, aminocarbonyl, (alkylamino)alkylaminocarbonyl,arylaminocarbonyl, heteroarylaminocarbonyl; or sulfonylcarbonyl);aryalkylcarbonyloxy; sulfonyl (e.g., alkylsulfonyl or aminosulfonyl);sulfinyl (e.g., alkylsulfinyl); sulfanyl (e.g., alkylsulfanyl); cyano;halo; hydroxyl; acyl; mercapto; sulfoxy; urea; thiourea; sulfamoyl;sulfamide; oxo; or carbamoyl. Alternatively, an aryl may beunsubstituted.

Examples of substituted aryls include haloaryl, alkoxycarbonylaryl,alkylaminoalkylaminocarbonylaryl, p, m-dihaloaryl,p-amino-p-alkoxycarbonylaryl, m-amino-m-cyanoaryl, aminoaryl,alkylcarbonylaminoaryl, cyanoalkylaryl, alkoxyaryl, aminosulfonylaryl,alkylsulfonylaryl, aminoaryl, p-halo-m-aminoaryl, cyanoaryl,hydroxyalkylaryl, alkoxyalkylaryl, hydroxyaryl, carboxyalkylaryl,dialkylaminoalkylaryl, m-heterocycloaliphatic-o-alkylaryl,heteroarylaminocarbonylaryl, nitroalkylaryl,alkylsulfonylaminoalkylaryl, heterocycloaliphaticcarbonylaryl,alkylsulfonylalkylaryl, cyanoalkylaryl,heterocycloaliphaticcarbonylaryl, alkylcarbonylaminoaryl,hydroxyalkylaryl, alkylcarbonylaryl, aminocarbonylaryl,alkylsulfonylaminoaryl, dialkylaminoaryl, alkylaryl, andtrihaloalkylaryl.

As used herein, an “aralkyl” group refers to an alkyl group (e.g., aC₁₋₄ alkyl group) that is substituted with an aryl group. Both “alkyl”and “aryl” are defined herein. An example of an aralkyl group is benzyl.A “heteroaralkyl” group refers to an alkyl group that is substitutedwith a heteroaryl.

As used herein, a “cycloalkyl” group refers to a saturated carbocyclicmono-, bi-, or tri-, or multicyclic (fused or bridged) ring of 3-10(e.g., 5-10) carbon atoms. Without limitation, examples of monocycliccycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl,cyclohexyl, cycloheptyl, or the like. Without limitation, examples ofbicyclic cycloalkyl groups include octahydro-indenyl,decahydro-naphthyl, bicyclo[3.2.1]octyl, bicyclo[2.2.2]octyl,bicyclo[3.3.1]nonyl, bicyclo[3.3.2.]decyl, bicyclo[2.2.2]octyl,bicycle[2.2.1]heptanyl, bicycle[3.1.1]heptanyl, or the like. Withoutlimitation, multicyclic groups include adamantyl, cubyl, norbornyl, orthe like. Cycloalkyl rings can be optionally substituted at anychemically viable ring position.

As used herein, a “heterocycloalkyl” group refers to a 3-10 memberedmono or bicyclic (fused or bridged) (e.g., 5 to 10 membered mono orbicyclic) saturated ring structure, in which one or more of the ringatoms is a heteroatom (e.g., N, O, S, or combinations thereof). Examplesof a heterocycloalkyl group include optionally substituted piperidyl,piperazyl, tetrahydropyranyl, tetrahydrofuryl, 1,4-dioxolanyl,1,4-dithianyl, 1,3-dioxolanyl, oxazolidyl, isoxazolidyl, morpholinyl,thiomorpholyl, octahydro-benzofuryl, octahydro-chromenyl,octahydro-thiochromenyl, octahydro-indolyl, octahydro-pyrindinyl,decahydro-quinolinyl, octahydro-benzo[b]thiopheneyl,2-oxa-bicyclo[2.2.2]octyl, 1-aza-bicyclo[2.2.2]octyl,3-aza-bicyclo[3.2.1]octanyl, 2,6-dioxa-tricyclo[3.3.1.0^(3,7)]nonyl,tropane. A monocyclic heterocycloalkyl group may be fused with a phenylmoiety such as tetrahydroisoquinoline. Heterocycloalkyl ring structurescan be optionally substituted at any chemically viable position on thering or rings.

A “heteroaryl” group, as used herein, refers to a monocyclic, bicyclic,or tricyclic ring structure having 4 to 15 ring atoms wherein one ormore of the ring atoms is a heteroatom (e.g., N, O, S, or combinationsthereof) and wherein one or more rings of the bicyclic or tricyclic ringstructure is aromatic. A heteroaryl group includes a benzofused ringsystem having 2 to 3 rings. For example, a benzofused group includesbenzo fused with one or two C₄₋₈ heterocyclic moieties (e.g., indolizyl,indolyl, isoindolyl, 3H-indolyl, indolinyl, benzo[b]furyl,benzo[b]thiophenyl, quinolinyl, or isoquinolinyl). Some examples ofheteroaryl are azetidinyl, pyridyl, 1H-indazolyl, furyl, pyrrolyl,thienyl, thiazolyl, oxazolyl, imidazolyl, tetrazolyl, benzofuryl,isoquinolinyl, benzthiazolyl, xanthene, thioxanthene, phenothiazine,dihydroindole, benzo[1,3]dioxole, benzo[b]furyl, benzo[b]thiophenyl,indazolyl, benzimidazolyl, benzthiazolyl, puryl, cinnolyl, quinolyl,quinazolyl, cinnolyl, phthalazyl, quinazolyl, quinoxalyl, isoquinolyl,4H-quinolizyl, benzo-1,2,5-thiadiazolyl, or 1,8-naphthyridyl.

II. Electrochemical Cells and Battery Stacks

Referring to FIGS. 1-23, in one aspect the present invention provides astatic (non-flowing) bipolar zinc-halide rechargeable electrochemicalcell 100 and battery stacks of such cells 1000.

A. Bipolar Electrochemical Cell

The bipolar electrochemical cell of the present invention 100 comprisesa bipolar electrode 102, a terminal assembly 104, and a zinc-halideelectrolyte.

1. Bipolar Electrodes

Bipolar electrodes 102, 102′ of present invention comprise a bipolarelectrode plate 208 having a front surface 212 and a back surface 214,wherein a cathode assembly 202 is affixed to the front surface of thebipolar electrode plate so that the cathode assembly electricallycommunicates with at least the front surface of the bipolar electrodeplate 208. Bipolar electrodes 102 of the present invention areconfigured to plate zinc metal on an anodic electrode surface (e.g., theback surface of an adjacent bipolar electrode or an inner surface of anendplate of a terminal anode assembly) and generate halide or mixedhalide species during charging of the electrochemical cell that arereversibly sequestered in the cathode assembly. Conversely, theseelectrodes are configured to oxidize plated zinc metal to generate Zn²⁺cations and reduce the halide or mixed halide species to theircorresponding anions during discharging of the electrochemical cell.

a. Bipolar Electrode Plates

Bipolar electrode plates of the present invention 208, 208′, comprise afront surface 212 and a back surface 214. The cathode assembly issituated on the front surface 212 (e.g., the cathodic surface) of thebipolar electrode plate 208. In some embodiments, the bipolar electrodeplate comprises a conductive material that is relatively inert to thezinc halide electrolyte used in the electrochemical cell or batterystack. In some embodiments, the bipolar electrode plate 208 comprises atitanium material (e.g., titanium or titanium oxide). In some instances,the bipolar electrode plate 208 further comprises a coating or film thatcovers at least a portion of the front surface 212, at least a portionof the back surface 214, or at least a portion of both surfaces. Inother embodiments, the bipolar electrode plate comprises a titaniummaterial that is coated with a titanium carbide material. In theseembodiments, at least a portion of the front surface 212, at least aportion of the back surface 214, or at least a portion of both surfacesare coated with the titanium carbide material. In some embodiments, thebipolar electrode plate comprises an electrically conductive carbonmaterial (e.g., a graphite plate). In some instances, the bipolarelectrode plate comprises a graphite plate that is coated with atitanium carbide material. In these embodiments, at least a portion ofthe front surface 212, the back surface 214, or at least a portion ofeither of these surfaces is coated with the titanium carbide material.

The bipolar electrode plate of the present invention optionallycomprises a recessed portion 215 on the front surface 212 of the bipolarelectrode plate. In some embodiments, the bipolar electrode platecomprises a recessed portion 215 on the front surface 212 of the bipolarelectrode plate. In some of these embodiments, peripheral edges of therecessed portion 215 are substantially defined by the outermost edge ofthe flange 220 of the cathode cage 216 of the cathode assembly 202, suchthat the cathode assembly at least partially fits within recessedportion 215 when the bipolar electrode is assembled. In otherembodiments, the peripheral edges of the recessed portion are at leastpartially within the outermost edge of the flange 220 of the cathodecage 216 of the cathode assembly 202. In some of these embodiments, therecessed portion may be defined by the outermost edge of the carbonmaterial 224 that is nested within the cathode cage 216 of the cathodeassembly 202, such that the carbon material 224 at least partially fitswithin recessed portion 215 of the bipolar electrode plate when thebipolar electrode 102 is assembled. And, in some alternativeembodiments, the front surface 212 of the bipolar electrode plate lacksa recessed portion such that the surface is at least substantially flat.

Bipolar electrode plates of the present invention may optionallycomprise one or more thru holes at or near the periphery 204 of theplate. Referring to FIGS. 2A-4, in some embodiments, the bipolarelectrode plate comprises one or more thru holes 206, 210 at or near theperiphery 204 of the plate that may be useful for filling anelectrochemical cell with liquid electrolyte or may be useful foraligning electrode plates in battery stacks.

The bipolar electrode plates may be formed by stamping or other suitableprocesses. A portion of the front surface 212, a portion of the backsurface 214, or portions of both surfaces may optionally undergo surfacetreatments (e.g., coating or the like) to enhance the electrochemicalproperties of the cell or battery stack. The back surface of the bipolarelectrode plate may include an electrochemically active regionassociated with or defined by the formation of a layer of zinc metalupon cell or battery stack charging. In some embodiments, the backsurface of the electrode plate may be sandblasted or otherwise treatedwithin the electrochemically active region. In other embodiments, thefront surface may also be sandblasted within an electrochemically activeregion associated with a region enclosed by the cathode assembly.

For example, in some embodiments, at least a portion of the backsurface, at least a portion of the front surface, or at least portionsof both surfaces are treated (e.g., sandblasted) to give a roughsurface. In some instances, at least a portion of the back surface ofthe bipolar electrode plate is treated (e.g., sandblasted) to give arough surface. In some instances, the region of the back surface that istreated to give a rough surface is substantially defined by theperiphery of the cathode assembly affixed to the front surface of theelectrode plate.

b. Cathode Assemblies

Electrochemical cells and battery stacks of the present inventioncomprise at least one cathode assembly 202, wherein the cathode assemblyis formed from a cathode cage 216, carbon material 224, and a separator222.

i. Cathode Cage

The cathode cage 216 comprises a pocket portion 218 and a flange 220 andis disposed on either the front surface 212, 212′ of the bipolarelectrode plate or the inner surface 316 of a terminal endplate at theflange 220. Referring to FIGS. 6A and 6B, a front view (FIG. 6A) and aside view (FIG. 6B) of the cathode cage 216 are illustrated. The cathodecage 216 includes an overall area defined by the length X₁ and the widthY₁ that includes the flange 220. To form the flanges, a flat metal sheetis installed in a forming machine to press the flanges on each of thefour edges of the flat sheet. In some implementations, the flat metalsheet comprises a titanium or titanium carbide material. In someembodiments, the cathode cage further comprises slots at the corners ofthe cage. These slots may be formed by laser cutting. The cathode cage216 includes a reduced area corresponding to the pocket portion 218defined by the length X₂ and the width Y₂. Accordingly, X₁ is greaterthan X₂ and Y₁ is greater than Y₂. In the example shown, the flange 220is flexed flat relative to the pocket portion 218 to dictate the X₁/X₂and Y₁/Y₂ dimensions and the depth of the pocket portion. In someembodiments, the area defined by X₂ and Y₂ is indicative of the etchingarea where a plurality of holes 227 are formed. Lengths X₁/X₂ and widthsY₁/Y₂ may vary based upon the operating requirements of theelectrochemical cell 100 or battery stack 1000.

In some embodiments, the flange 220 includes a surface adjacent to andcontacting the front surface 212 of the bipolar electrode plate and adepth of the pocket portion 218 extends from the flange in a directionaway from the front surface of the electrode plate. The pocket portion218 of the cathode cage operates cooperatively with the front surface ofthe electrode plate to form a chamber in which the separator 222 and thecarbon material 224 are situated. In some of these embodiments, thecathode cage is disposed on the front surface of the electrode plate atits flange by welding, use of an adhesive, use of a mechanical fastener,or any combination thereof.

The cathode cage is formed of a metal or metal alloy that issubstantially inert to the electrolyte of the electrochemical cell orbattery stack. In some embodiments, the cathode cage is stamped from atitanium material (e.g., titanium or titanium oxide). In otherembodiments, the cathode cage comprises a titanium material that iscoated with a titanium carbide material.

In some embodiments, the pocket portion of the cathode cage ischemically-etched to form a plurality of spaced holes 227. In someembodiments, the holes are sized and spaced to form a hole pattern(e.g., a modulated hole pattern) that increases the uniformity ofcurrent and/or charge distributed across the cathode cage bycompensating for the deformation or bending of the pocket portion of thecathode cage that occurs during operation (e.g., charging ordischarging) of the electrochemical cell.

FIG. 7A illustrates the front view of the cathode cage 216 depicted byFIG. 6A, including the plurality of holes 227 formed through thechemically-etched surface of the pocket portion 218 by chemical etching.FIG. 7B is a detailed view of a portion illustrated by FIG. 7A showing adistribution of the plurality of holes 227. The chemical etching processis a subtractive manufacturing process that eliminates solid materialthat is to be removed for forming the plurality of holes 227. During thefirst step of the chemical etching process, the cathode cage 216 beginsas a flat metal sheet that is cut using a shear to achieve dimensionscorresponding to X₁ and Y₁. Next, the metal sheet may be cleaned andcoated with a dry film solder mask in a hot roll laminator and thencooled in a dark environment. A protective film may then be appliedwithin a vacuum exposure unit to expose the metal sheet. In someexamples, the magnitude of exposure may be measured using a stepindicator, and the exposure is determined when a desired magnitude ofexposure is achieved. Subsequently, the metal sheet is run through adeveloper to remove the protective film while a resolve detergent in thedeveloper is applied to the metal sheet to remove unwanted, unexposedresist. The metal sheet may then be placed in a furnace rack and bakedat a predetermined temperature for a predetermined period of time. Forinstance, the baking temperature may be about 250° F. for about 60minutes. Following the baking cycle, each metal sheet is air-cooled, anda chemical etching device is programmed for specifications of thedesired etching area, e.g., the area defined by X₂ and Y₂, and the bakedand cooled metal sheet is run through the chemical etching device toremove the unwanted material and thereby form the holes 227.

Referring now to FIG. 7B, the plurality of holes 227 are spaced anddistributed along rows in a pattern. In some embodiments, the pattern isan alternating repeating pattern. In some embodiments, the pattern isselected to permit a uniform distribution of current across the cathodecage 216 in the presence of the cathode cage bending and deforming fromflat during charging of the electrochemical cell or battery stack. Alsoreferring to FIGS. 30A-31C, providing the cathode cage with a holepattern in accordance with the present invention enhances the uniformdistribution of charge and/or current which generates a more uniformplating of zinc metal at the anodic surface (e.g., the back surface 214of a bipolar electrode plate, or the inner surface 318 of an endplate,or both surfaces) of the bipolar electrode plate during charge cycles.Likewise, conversions between bromine and bromide anions at or near thecathode cage 216 may also be enhanced. In some embodiments, the spacingbetween each hole of the plurality of holes 227 along the rows in thex-direction, the spacing between the alternating rows in they-direction, and the diameter, p, of the holes may be selected toachieve a substantially uniform distribution of charge and/or currentacross the cathode cage 216 based on the amount of bend or deformationthat results in the cathode cage and the bipolar electrode the when theelectrochemical cell or battery stack undergoes charging anddischarging. In some implementations, the distribution of the x and yhole locations (e.g., spacing) in each of the x and y directions isbased upon a nominal hole area and a recommended web length of thecathode cage 216. The thickness of the surface of the pocket portion 218may dictate the dimensions of the nominal hole area and the recommendedweb length. In some examples, the center of the adjacent plurality ofholes 227 along a row are spaced by about 0.067 cm in the x-directionand every other row is spaced by about 0.152 cm in the y-direction. Asdescribed in greater detail below, the cathode cage 216, and the bipolarelectrode plate 208, 208′, or the terminal endplate 302 will bendgreater distances from flat at regions further from the perimeter ateach of the parts resulting in the spacing between the anode and cathodeelectrodes to be shorter at the center regions with respect the outerregions near the perimeter. Generally, as the spacing between the anodeand cathode electrodes decreases, the calculated hole diameter atcorresponding x and y hole locations will increase.

In some embodiments, the spacing between the electrodes (e.g., betweenthe cathode cage 216 and the back surface 214 or the inner surface 318of the bipolar electrode plate 208, 208′, 302) is calculated at each ofthe plurality of evenly distributed x and y hole locations along theetching area (e.g., area defined by X₂ and Y₂) of the cathode cage. Anx-y origin can include the lower left boundary of the pocket portion 218shown in FIG. 7B where the x- and y-axis intersect. Thereafter, the holearea for each of the plurality of holes 227 may be calculated based onthe calculated spacing between the cathode and anode electrodes at eachof the x and y locations, a predetermined minimum spacing between theelectrodes, and the nominal hole area. In some embodiments, the numberof the plurality of holes 227 can be further based upon the thickness ofthe surface of the pocket portion 218 of the cathode cage 216. In someexamples, the predetermined minimum spacing is about 7.45 mm and thenominal hole area is about 1.08 mm². In some implementations,calculating the spacing between the anode and cathode electrodes at eachof the plurality of x and y locations along the etching area iscalculated using the following fit equation:

f=y0+a*x+b*y+c*x ² +d*y ²  [1].

The coefficients for the fit equation of Eq. [1] may be determined bymeasuring a delta from flat for each cathode cage 216 and, the electrodeplate 208′ or terminal endplate 302 for each of bipolar electrodes. Themeasurement is taken from the plurality of x and y hole locations acrosseach of the cathode cage 216 and corresponding locations at theelectrode plate 208′. An average is calculated for each of the pluralityof bipolar electrodes 102, for both the cathode cage 216, and theelectrode plate 208′ or the terminal endplate 302, at each location.Data corresponding to the calculated averages is utilized to determinethe coefficients y0, a, b, c, and d for each of the cathode cage and theelectrode plate. In some embodiments, the direction of the delta foreach of the two electrodes is adjusted so that the flat distance betweenthe two is a desired spacing, e.g., about 10.0 mm, and the delta for theelectrode plate extends up from about 0 mm and the delta for the cathodecage extends down from about 10.0 mm. Accordingly, the coefficientsdetermined for each of the electrode plate and the cathode cage are asfollows:

Electrode Plate/Terminal Endplate

-   -   y0=−1.5787    -   a=0.8948    -   b=2.4920    -   c=−0.1268    -   d=−0.9132

Cathode Cage

-   -   y0=10.8602    -   a=−0.5295    -   b=−1.5860    -   c=0.0814    -   d=0.6857

New coefficients put into the fit equation of Eq. [1] may be determinedby subtracting the anode coefficients from the cathode coefficients.Accordingly, the new coefficients for input into Eq. [1] are as follows:

-   -   y0=12.4389    -   a=−1.4243    -   b=−4.078    -   c=0.2082    -   d=1.5989

The x and y hole locations must be normalized by the etching area beforebeing input to Eq. [1] for calculating the spacing of the plurality ofholes 227. For instance, each x location is divided by the length, X₂,of pocket portion 218 and each y location is divided by the width, Y₂,of the pocket portion. Thereafter, each normalized x and y holelocation, along with the new coefficients determined above, are input toEq. [1] to determine the spacing between the anode and the cathodeelectrodes at each x and y hole location. The fit equation of Eq. [1] isa non-linear three-dimensional paraboloid equation. In someimplementations, Eq. [1] is executed using SigmaPlot™ software licensedby Systal Software, Inc.

In some implementations, the area of each hole of the plurality of holes227 at each x and y location may be calculated as follows:

$\begin{matrix}{\phi_{x,y} = {f \times \frac{A_{nominal}}{S_{{nominal}\_ {minimum}}}}} & \lbrack 2\rbrack\end{matrix}$

-   -   wherein        -   φ_(x,y) is the calculated diameter at each hole location,        -   f is the spacing between the electrodes at each hole            location calculated utilizing Eq. 1,        -   A_(nominal) is the nominal hole area, and        -   S_(nominal) _(_) _(minimum) is the nominal minimum hole            spacing.

In some examples, the nominal hole area is about 1.08 mm² and thenominal minimum spacing is about 7.45 mm². The examples for calculatingthe hole diameter utilize mixed units, wherein inches are utilized foreach of the x and y hole locations and the etching area defined by X₂and Y₂ while millimeters are utilized for calculating the spacingbetween the electrodes. Equation [2] demonstrates that the hole diameterincreases as the spacing between the anode and cathode electrodesincreases. The average hole diameter calculated at each hole locationutilizing Eq. 2 for each of the bipolar electrodes 102, 102′ isaveraged. Implementations include utilizing the average hole diameterfor the plurality of holes 227 formed in the cathode cage 216 for eachof the plurality of bipolar electrodes 102, 102′.

FIGS. 10 and 11 illustrate experimental data of average spacing betweenthree dimensional shape profiles of the bipolar electrode plate 208′ andthe cathode cage 216 with respect to the x-axis (FIG. 10) and the y-axis(FIG. 11). The experimental data illustrates an average taken fromtwenty bipolar electrodes 102, 102′ of the battery module 1000. Theelectrode plate 208′ and the cathode cage 216 bend from flat whencharged. In the example shown, the cathode cage and the electrode plateare arranged such that the spacing between the cathode cage and theelectrode plate from flat is about 10 mm with respect to the z-axis. Theelectrode plate has a largest delta from flat of about 1.566 mm alongthe z-axis at direct center (e.g., about 3.5 mm with respect to thex-axis) and the cathode cage has a largest delta from flat of about0.565 mm along the x-axis at right-center (e.g., about 2.0 mm withrespect to the x-axis). An average electrode separation from left-centerto right-center of plurality of bipolar electrodes is about 7.78 mm.

ii. Carbon Material

The carbon material 224 is in electrical communication with the frontsurface 212, 212′ of the bipolar electrode plate 208, 208′ and isconfined by the cathode cage 216, 216′, the separator 222, and the frontsurface 212, 212′ of the bipolar electrode plate. Carbon materialssuitable for electrochemical cells of the present invention may compriseany carbon material that can reversibly absorb aqueous bromine species(e.g., aqueous bromine or aqueous bromide) (collectively 702) and issubstantially chemically inert in the presence of the electrolyte. Insome embodiments, the carbon material comprises carbon blacks or otherfurnace process carbons. Suitable carbon black materials include, butare not limited to, Cabot Vulcan® XC72R, Akzo-Nobel Ketjenblack EC600JD,and other matte black mixtures of conductive furnace process carbonblacks. In some embodiments, the carbon material may also include othercomponents, including but not limited to a PTFE binder and de-ionizedwater. For example, the carbon material has a water content of less than50 wt % (e.g., from about 0.01 wt % to about 30 wt %) by weight of thecarbon material. In some embodiments, the carbon material comprises PTFE(e.g., from about 0.5 wt % to about 5 wt % by weight of the carbonmaterial).

In some embodiments, the carbon material is molded into a size and shapesuch that the carbon material can be at least partially nested by thecathode cage. In some examples, the carbon material may be in the formof one or more thin rectangular blocks. For instance, the carbonmaterial is formed into one or more thin rectangular blocks havingrounded corners such that the corners do not perforate the separatorwhen the cathode assembly is assembled. In some embodiments, the carbonmaterial may comprise a single solid block. In other embodiments, thecarbon material may comprise from one to five, one to three, or one totwo solid blocks of carbon blacks.

iii. Separator

Separators 222 useful in the electrochemical cells or battery stacks ofthe present invention are capable of forming a porous barrier between atleast the reduced surface of the pocket portion of the cathode cage andthe carbon material. In some embodiments, the separator is formed of awettable woven or wettable non-woven cloth. And, in some examples, thewoven or non-woven cloth comprises a plurality of pores that are sizedto permit the passage of electrolyte therethrough while at leastsubstantially restraining the passage of particles of carbon materialtherethrough. In other embodiments, the separator is formed from acarbon cloth including Zorflex® FM10 ACC 100% activated woven carboncloth having with an extremely large surface area (e.g., 1000-2000 m²/g)and/or exhibits rapid reaction and adsorption kinetics.

In some embodiments, the separator 222 is interposed between at least aportion of the cathode cage and the carbon material. And, in otherembodiments, the separator substantially wraps the carbon material suchthat the separator is interposed between the carbon material andsubstantially all of the pocket portion of the cathode cage, and theseparator is interposed between at least a portion of the carbonmaterial and at least a portion of the bipolar electrode plate. Forexample, the separator is interposed between at least the reducedsurface of the pocket portion of the cathode cage possessing a holepattern (e.g., a plurality of holes 227) and the carbon material.

2. Terminal Assembly

Another aspect of the present invention provides a terminal assembly fora bipolar electrochemical cell or a battery. Referring to FIGS. 12-17, aterminal assembly 104 of the present invention comprises a conductivecup-shaped member 310 that comprises a terminal wall 312, a sidewall304, and a rim 306 that is separated from the terminal wall by thesidewall. A terminal 308 of the bipolar electrochemical cell or batterystack is connected for electrical communication with the terminal wall312 of the conductive cup-shaped member 310. In some embodiments, theterminal 308 comprises brass (e.g., the terminal is a brass plug thatelectrically communicates or contacts the terminal wall). In someembodiments, a portion of the terminal wall 312 in contact with theterminal 308 comprises copper. In these embodiments, the terminal wallmay be formed from titanium and include a copper plate operative tocontact and electrically connect the terminal formed from copper to theterminal wall of the conductive cup-shaped member.

The terminal assembly further comprises a terminal endplate 302 havinginner and outer surfaces 318, 316 at least substantially coplanar withthe terminal wall and joined to the rim at the outer surface 316. Theterminal endplate 302 may be formed to comprise any of the featurespresent in the bipolar electrode plate, including without limitation, atitanium material that is coated with a titanium carbide material, thruholes, rough inner surface, or the like. The rim of the cup-shapedmember joins to the terminal endplate 302 such that the rim isapproximately centered about the electrochemically active region 322 ofthe terminal endplate. In some embodiments, the electrochemically activeregion 322 corresponds to a region extending between the inner and outersurfaces of the terminal endplate in chemical or electricalcommunication with the adjacent bipolar electrode during charge anddischarge cycles of the electrochemical cell or battery stack. In theseembodiments, the electrochemically active region for the terminalendplate associated with the negative cathode terminal of the batterycorresponds to or is defined by an area enclosed by a cathode assemblydisposed upon the inner surface of the terminal endplate (e.g., theterminal cathode endplate). The electrochemically active region for theterminal endplate associated with the positive anode terminal of thebattery may correspond to an area on its inner surface that opposes acathode assembly disposed on the front surface of an adjacent bipolarelectrode plate and forms a layer of zinc metal upon charging of thebattery (terminal anode assembly). In some embodiments, at least aportion of the inner surface (e.g., at least the chemically activeregion) of the terminal endplate of the terminal anode assembly is arough surface.

FIG. 14 provides a top view of the terminal endplate showing theelectrochemically active region of the terminal endplate comprising afirst surface area 326 enclosed within dashed ellipse 306 correspondingto the outer periphery of the rim and a remaining second surface area324 defined by the outer periphery of the rim 306 and the peripheraledges of the electrochemically active region 322. The conductivecup-shaped member 310 is removed for clarity in FIG. 14 so that thefirst surface area can be shown. Thus, the first surface area isenclosed by the rim when the conductive cup-shaped member is joined tothe outer surface of the terminal endplate. The first 326 and second 324surface areas are substantially equal.

In some embodiments, the rim is substantially elliptical and defined bya major axis A_(MAJ) and a minor axis A_(MIN) perpendicular to the majoraxis, the major axis and the minor axis intersecting at a center of therim and also the center of the electrochemically active region. As usedherein, the substantially elliptical rim refers to the rim having asubstantially rectangular shape with radiused, or otherwise curved androunded corners. In some embodiments, the rim is substantiallyrectangular. FIG. 15 provides a cross-sectional view taken along line15-15 of FIG. 13 showing a major radius R_(MAJ) of the rim beingsubstantially equal to a first distance D1 extending along the majoraxis from the outer periphery of the rim to a peripheral edge of theelectrochemically active region that is parallel to the minor axis; andFIG. 13 shows a minor radius R_(MIN) of the rim is substantially equalto a second distance D2 extending along the minor axis from the outerperiphery of the rim to a peripheral edge of the electrochemicallyactive region that is parallel to the major axis.

In some embodiments, the rim defines an opening of an interior region330 defined by interior surfaces of the terminal wall and the sidewall,and the outer surface of the terminal endplate enclosing the opening ofthe interior region when joined to the rim.

In some embodiments, the rim is centered within the electrochemicallyactive region of the endplate. In some embodiments, the rim issubstantially circular or substantially elliptical.

In some embodiments, the sidewall is perpendicular or substantiallyperpendicular to the terminal wall and the rim. In other embodiments,the sidewall extends radially outward from the terminal wall to the rim.

In some embodiments, the rim is substantially circular. For example,FIG. 16 provides a top perspective view of the terminal assemblycomprising the conductive cup-shaped member that comprises the terminalwall, the sidewall, and a substantially circular rim 306′ that isseparated from the terminal wall by the sidewall. In these embodiments,a radius R1 of the rim is substantially equal to a distance D3 betweenperipheral edges of the electrochemically active region 322 and theouter periphery of the rim.

Referring to FIG. 17, a cross-sectional view taken along 17-17 of FIG.13 shows the terminal assembly comprising the conductive cup-shapedmember, the terminal endplate, an optional frame member 114, and abipolar electrode that is immediately adjacent to the terminal assemblywherein the bipolar electrode comprises a cathode assembly 202 and abipolar electrode plate 208. Referring to FIGS. 17 and 23, in someembodiments, the frame member 114 comprises a first side 614 and asecond side 616, the first side opposed to and receiving the innersurface 318 of the terminal endplate 302 on a side opposite theconductive cup-shaped member 312. In some of these embodiments, thesecond side of the frame member opposes the cathode assembly 202 of thebipolar electrode, and the bipolar electrode comprises a bipolarelectrode plate 208 comprising a front surface 212 fastened to thesecond side 616 of the frame member; and a cathode assembly 202 situatedon the front surface of the bipolar electrode plate, the cathodeassembly interposed between the front surface of the bipolar electrodeplate and the inner surface of the terminal endplate. In someembodiments, the electrochemically active region 322 situated at theinner surface of the terminal endplate opposes the cathode assemblysituated on the front surface of the bipolar electrode plate andincludes a size and shape that is substantially the same as a size andshape of the cathode assembly. Discussed in greater detail above withreference to FIGS. 3 and 4B, the cathode assembly 202 comprises acathode cage 216, a separator 222, and a carbon material 224 situated onthe front surface 212, 212′ of the bipolar electrode plate.

In some embodiments, the terminal assembly is a terminal cathodeassembly, wherein the terminal cathode assembly comprises a terminalendplate 302 having an electrochemically active region, a conductivecup-shaped member such as any of the cup shaped members described hereindisposed on the outer surface of the terminal endplate and approximatelycentered in the electrochemically active region, and a cathode assemblysuch as any of the cathode assemblies described herein disposed on theinner surface of the terminal endplate.

In some embodiments, the terminal assembly comprises a terminal anodeassembly, wherein the terminal anode assembly comprises a terminalendplate having an electrochemically active region, a conductivecup-shaped member such as any of the cup shaped members described hereindisposed on the outer surface of the terminal endplate and approximatelycentered in the electrochemically active region, and wherein theterminal anode assembly lacks a cathode assembly.

In some embodiments, the rim of the conductive cup-shaped member isjoined to the outer surface of the terminal endplate by a weld or anadhesive. In some instances, the adhesive is electrically conductive.Examples of suitable electrically conductive adhesives include graphitefilled adhesives (e.g., graphite filled epoxy, graphite filled silicone,graphite filled elastomer, or any combination thereof), nickel filledadhesives (e.g., nickel filled epoxy), silver filled adhesives (e.g.,silver filled epoxy), copper filled adhesives (e.g., copper filledepoxy), any combination thereof, or the like.

In some embodiments, the conductive cup-shaped member is composed of atleast one of a copper alloy, a copper/titanium clad, aluminum, andelectrically conductive ceramics. For instance, the interior surfaces ofthe terminal wall and the sidewall comprise copper. In other instances,the exterior surfaces of the terminal wall and the sidewall comprise atleast one of copper, titanium, and electrically conductive ceramics.

In some embodiments, at least one of the conductive cup-shaped member orthe terminal endplate comprises titanium. In some embodiments, at leastone of the conductive cup-shaped member or the terminal endplatecomprises a titanium material coated with a titanium carbide material.

In some embodiments, the conductive cup-shaped member comprises a firstmetal and the endplate comprises a second metal.

In some embodiments, the rim comprises a flange 328 (FIG. 15) extendingradially outward from the sidewall.

Referring again to FIG. 15, electrical properties of an exemplaryterminal assembly for a zinc-halide electrochemical cell or batterystack during its operation (e.g., charging or discharging) aregeneralized according to the following expressions:

V _(A) ≈V _(E) ≈V _(C)  exp. 1

V _(D) ≈V _(B)  exp. 2

V _(F) ≈V _(G)  exp. 3

ΔV _(G-D) ≈ΔV _(F-B) >>ΔV _(H-G) ≈ΔV _(F-H)  exp. 4

ΔV _(G-D) ≈ΔV _(F-B) >>ΔV _(B-C) ≈ΔV _(D-C)  exp. 5

B and D identify two electrical points of contact between the rim of thecup-shaped member and the first surface of the bipolar endplate. Hrepresents the center of inversion of symmetry for the conductivecup-shaped member, and C represents the superposition of H onto thefirst surface of the bipolar endplate such that the line CH extendingalong the minor axis A_(MIN) and joining C and H is normal to the firstsurface of the endplate. F and G identify junctions where the terminalwall 312 and the sidewall 304 meet, and A and E identify opposingperipheral edges of the electrochemically active region 322.

The charge at A, V_(A), is approximately equal to the charges at E,V_(E), and C, V_(C). The charge at D, V_(D), is approximately equal tothe charge at B, V_(B). The charge at F, V_(E), is approximately equalto the charge at G, V_(G). The electrical potential difference, orvoltage from G to D, ΔV_(G-D), is approximately equal to the voltagefrom F to B, ΔV_(F-B), the voltage from H to G, ΔV_(H-G) isapproximately equal to the voltage from F to H, ΔV_(F-H), and ΔV_(G-D)and ΔV_(F-B) is substantially greater than ΔV_(H-G) and ΔV_(F-H). And,the voltages ΔV_(G-D) and ΔV_(F-B) are substantially greater than thevoltages from B to C, ΔV_(B-C), and D to C, ΔV_(D-C).

Because the voltages from G to D and from F to B, i.e., ΔV_(G-D) andΔV_(F-B), are substantially greater than the voltage from H to G and Fto H, i.e., ΔV_(H-G) and ΔV_(F-H), current discharged from the terminalof the terminal assembly of the present invention is substantially moreuniform than discharge current from a traditional bipolar battery havinga terminal directly attached to an endplate.

3. Zinc-Halide Electrolyte

In electrochemical cells and battery stacks of the present invention, anaqueous electrolyte, i.e., a zinc-halide electrolyte is interposedbetween the inner surface of the terminal endplate, the cathodeassembly, the front surface of the bipolar electrode, and if present,the interior surfaces of the frame. In these embodiments, bromide anionsat the surface of the cathode cage of the cathode assembly that isexposed to the electrolyte are oxidized to bromine when theelectrochemical cell or battery stack is charging. Conversely, duringdischarge, the bromine is reduced to bromide anions. The conversionbetween bromine and bromide anions 232 at or near the cathode cage ofthe cathode assembly can be expressed as follows:

Br₂+2e ⁻→2Br⁻.

The present invention provides an aqueous electrolyte that is useful inflowing or non-flowing (i.e., static) rechargeable zinc halideelectrochemical cells or battery stacks. In these cells or batterystacks, zinc bromide, zinc chloride, or any combination of the two,present in the electrolyte, acts as the electrochemically activematerial.

One aspect of the present invention provides an electrolyte for use in asecondary zinc bromine electrochemical cell comprising from about 30 wt% to about 40 wt % of ZnBr₂; from about 5 wt % to about 15 wt % of KBr;from about 5 wt % to about 15 wt % of KCl; and one or more quaternaryammonium agents, wherein the electrolyte comprises from about 0.5 wt %to about 10 wt % of the one or more quaternary ammonium agents.

In some embodiments, the electrolyte comprises from about 4 wt % toabout 12 wt % (e.g., from about 6 wt % to about 10 wt %) of potassiumbromide (KBr). In some embodiments, the electrolyte comprises from about8 wt % to about 12 wt % of potassium bromide (KBr).

In some embodiments, the electrolyte comprises from about 4 wt % toabout 12 wt % (e.g., from about 6 wt % to about 10 wt %) of potassiumchloride (KCl). In some embodiments, the electrolyte comprises fromabout 8 wt % to about 14 wt % of potassium chloride (KCl). In someembodiments, the electrolyte comprises from about 11 wt % to about 14 wt% of potassium chloride (KCl).

In some embodiments, the electrolyte further comprises from about 0.5 wt% to about 10 wt % (e.g., from about 1 wt % to about 7.5 wt %) of aglyme. In some examples, the glyme comprises monoglyme, diglyme,triglyme, tetraglyme, pentaglyme, hexaglyme, or any combination thereof.For instance, the glyme comprises tetraglyme. In other examples, theelectrolyte comprises from about 1 wt % to about 5 wt % of tetraglyme.

In some embodiments, the electrolyte further comprises from about 0.05wt % to about 4 wt % (e.g., from about 0.1 wt % to about 1 wt %) of anether. In some embodiments, the ether is a crown ether, DME-PEG,dimethyl ether, or any combination thereof. In a further embodiment, theether is a crown ether.

In some embodiments, the electrolyte further comprises from about 0.5 wt% to about 2.5 wt % (e.g., from about 1 wt % to about 2.25 wt %) ofDME-PEG or dimethyl ether. In some examples, the DME-PEG has an averagemolecular weight (e.g., a number average molecular weight M_(n)) of fromabout 350 amu to about 3000 amu. In other examples, the DME-PEG has anaverage molecular weight of from about 1200 amu to about 3000 amu. And,in some examples, the electrolyte further comprises from about 5 wt % toabout 10 wt % of DME-PEG, wherein the DME-PEG has an average molecularweight (e.g., a number average molecular weight M_(n)) of from about1500 amu to about 2500 amu (e.g., about 2000 amu).

In some embodiments, the ether is a crown ether. For example, the crownether is 18-crown-6. For example, the crown ether is 15-crown-5. Forexample, the crown ether is 12-crown-4.

In some embodiments, the electrolyte further comprises from about 0.1 wt% to about 1.0 wt % of an alcohol, wherein the alcohol is substantiallymiscible in water. For example, the alcohol comprises a C₁₋₄ alcohol. Inother examples, the alcohol comprises methanol, ethanol, 1-propanol(i.e., n-propanol), 2-propanol (i.e., iso-propanol), 1-butanol (i.e.,n-butanol), sec-butanol, iso-butanol, tert-butanol, 1-pentanol, or anycombination thereof. And in some examples, the electrolyte furthercomprises from about 0.25 wt % to about 0.75 wt % of tert-butanol.

In some embodiments, the electrolyte further comprises from about 0.25wt % to about 5 wt % (e.g., from about 0.5 wt % to about 4 wt %) of aC₁₋₁₀ glycol. In some examples, the electrolyte further comprises fromabout 0.25 wt % to about 5 wt % (e.g., from about 0.5 wt % to about 4 wt%) of a substituted ethylene glycol or a substituted propylene glycol.In some examples, the glycol comprises ethylene glycol, propyleneglycol, 1,3-butylene glycol, 1,4-butylene glycol, neopentyl glycol,hexalene glycol, or any combination thereof. And, in some examples, theelectrolyte further comprises from about 0.25 wt % to about 2.5 wt % ofneopentyl glycol.

In some embodiments, the one or more quaternary ammonium agents is asalt of Formula I

wherein

is saturated, partially unsaturated, or fully unsaturated;

-   -   X₁, X₂, X₃, X₄, and X₅ are each independently selected from        carbon, oxygen, and nitrogen, provided that at least one of X₁,        X₂, X₃, X₄, and X₅ is nitrogen;    -   each R is independently hydrogen, alkyl, cycloalkyl, aryl,        arylalkyl, heterocycloalkyl, or heteroaryl, wherein each R is        independently and optionally substituted with halo, —CN, —NO₂,        —OQ₂, —S(O)_(z)Q₂, —S(O)_(z)N(Q₂)₂, —N(Q₂)₂, —C(O)OQ₂, —C(O)Q₂,        —C(O)N(Q₂)₂, —C(O)N(Q₂)(OQ₂), —N(Q₂)C(O)Q₂, —N(Q₂)C(O)N(Q₂)₂,        —N(Q₂)C(O)OQ₂, —N(Q₂)S(O)_(z)Q₂, or heterocycloalkyl or alkyl        optionally substituted with 1-3 Q₃ substituents;    -   each Q₂ is independently hydrogen, alkyl, cycloalkyl, aryl,        arylalkyl, heterocycloalkyl, or heteroaryl, each optionally        substituted with 1-3 Q₃ substituents;    -   each Q₃ is independently halo, oxo, CN, NO₂, CF₃, OCF₃, OH,        —S(O)_(z)(C₁₋₆ alkyl), —N(C₁₋₆ alkyl)₂, —COO(C₁₋₆ alkyl), —C(O)        (C₁₋₆ alkyl), —O(C₁₋₆ alkyl), or a C₁₋₆ alkyl optionally        substituted with 1-3 substituents selected from halo, oxo, —CN,        —NO₂, —CF₃, —OCF₃, —OH, —SH, —S(O)_(z)H, —NH₂, or —COOH;    -   m is 0, 1, 2, 3, 4, or 5;    -   n is 0, 1, or 2; and    -   Y is an anion.

In one embodiment, one or two of X₁, X₂, X₃, X₄, and X₅ are nitrogen,and the rest are carbon. In a further embodiment, one of X₁, X₂, X₃, X₄,and X₅ is nitrogen, and the rest are carbon. In another furtherembodiment, two of X₁, X₂, X₃, X₄, and X₅ are nitrogen, and the rest arecarbon. In still a further embodiment,

is selected from pyridine, pyrimidine, pyrazine, piperazine, piperidine,morpholine, 1,3-oxazinane, 1,2-oxazinane, pyrrolidine, pyrrole,pyrazole, imidazole, oxazole, isoxazole, 1,2,3-oxadiazole,1,3,4-oxadiazole, 1,2,3-triazole, 1,2,4-triazole, 1,2,3,4-oxatriazole,1,2,3,5-oxatriazole, 1,2,4,5-oxatriazole, and tetrazole.

In one embodiment,

is selected from pyridine, pyrimidine, pyrazine, piperazine, piperidine,morpholine, 1,3-oxazinane, and 1,2-oxazinane. In one embodiment,

is selected from pyridine, pyrimidine, and pyrazine. In a furtherembodiment,

is pyridine.

In one embodiment,

is selected from piperidine, morpholine, 1,3-oxazinane, and1,2-oxazinane. In a further embodiment

is selected from piperidine and morpholine. In one embodiment,

is piperidine. In one embodiment

is morpholine.

In one embodiment,

is selected from pyrrolidine, pyrrole, pyrazole, imidazole, oxazole,isoxazole, 1,2,3-oxadiazole, 1,3,4-oxadiazole, 1,2,3-triazole,1,2,4-triazole, 1,2,3,4-oxatriazole, 1,2,3,5-oxatriazole,1,2,4,5-oxatriazole, and tetrazole. In another embodiment,

is selected from pyrrole, pyrazole, and imidazole. In one embodiment

is pyrrole. In one embodiment

is pyrazole. In one embodiment,

is imidazole. In one embodiment,

is pyrrolidine.

In one embodiment, n is 1. In another embodiment, n is 0.

In one embodiment, each R is independently alkyl or cycloalkyl, whereineach R is independently and optionally substituted with halo, —CN, —NO₂,—OQ₂, —S(O)_(z)Q₂, —S(O)_(z)N(Q₂)₂, —N(Q₂)₂, —C(O)OQ₂, —C(O)Q₂,—C(O)N(Q₂)₂, —C(O)N(Q₂)(OQ₂), —N(Q₂)C(O)Q₂, —N(Q₂)C(O)N(Q₂)₂,—N(Q₂)C(O)OQ₂, —N(Q₂)S(O)_(z)Q₂, or heterocycloalkyl or alkyl optionallysubstituted with 1-3 Q₃ substituents. In another embodiment, each R isindependently alkyl or cycloalkyl, wherein each R is independently andoptionally substituted with halo, heterocycloalkyl, —CN, —NO₂, —OQ₂,—N(Q₂)₂, —C(O)OQ₂, —C(O)Q₂, or —C(O)N(Q₂)₂. In a further embodiment,each R is alkyl, which is independently and optionally substituted withhalo, heterocycloalkyl, —CN, —NO₂, —OQ₂, —N(Q₂)₂, —C(O)OQ₂, —C(O)Q₂, or—C(O)N(Q₂)₂. In still a further embodiment, each R is alkyl, which isindependently and optionally substituted with halo, heterocycloalkyl,—CN, —NO₂, —N(Q₂)₂, or —C(O)N(Q₂)₂. In yet a further embodiment, each Ris alkyl, which is independently and optionally substituted with halo orheterocycloalkyl.

In another embodiment, each R is alkyl, which is substituted withheterocycloalkyl. In a further embodiment, R is alkyl, which issubstituted with pyrrolidine. In a further embodiment, R is propyl,which is substituted with heterocycloalkyl. In a further embodiment, Ris propyl, which is substituted with pyrrolidine.

In one embodiment, each R is an unsubstituted alkyl. In anotherembodiment, R is selected from methyl, ethyl, propyl, isopropyl, butyl,isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, 2-ethylhexyl,octyl, nonyl, decyl, dodecyl, and cetyl. In one embodiment, R isselected from methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl,octyl, nonyl, decyl, dodecyl, and cetyl. In one embodiment, R is methyl.In one embodiment, R is ethyl. In one embodiment, R is propyl. In oneembodiment, R is butyl. In one embodiment, R is pentyl. In oneembodiment, R is hexyl. In one embodiment, R is heptyl. In oneembodiment, R is octyl. In one embodiment, R is dodecyl. In oneembodiment, R is nonyl. In one embodiment, R is decyl. In oneembodiment, R is dodecyl. In one embodiment, R is cetyl.

In one embodiment, Y is an anion selected from fluoride, chloride,bromide, iodide, arsenate, phosphate, arsenite, hydrogen phosphate,dihydrogen phosphate, sulfate, nitrate, hydrogen sulfate, nitrite,thiosulfate, sulfite, perchlorate, iodate, chlorate, bromate, chlorite,hypochlorite, hypobromite, carbonate, chromate, hydrogen carbonate(bicarbonate), dichromate, acetate, formate, cyanide, amide, cyanate,peroxide, thiocyanate, oxalate, hydroxide, and permanganate. In afurther embodiment, Y is a monovalent anion selected from fluoride,chloride, bromide, iodide, dihydrogen phosphate, nitrate, perchlorate,hypochlorite, hydrogen carbonate (bicarbonate), acetate, formate,cyanide, and hydroxide. In another further embodiment, Y is a bivalentanion selected from hydrogen phosphate, sulfate, and carbonate. In stilla further embodiment, Y is selected from fluoride, chloride, bromide andiodide. In one embodiment, Y is chloride. In one embodiment, Y isbromide. In one embodiment, Y is iodide.

In some embodiments, the one or more quaternary ammonium agents is asalt of Formula Ia, Formula Ib, Formula Ic, Formula Id, or Formula Ie

wherein

each R, R′, and R″ is independently hydrogen, alkyl, cycloalkyl, aryl,arylalkyl, heterocycloalkyl, or heteroaryl, wherein each R, R′, and R″is independently and optionally substituted with halo, —CN, —NO₂, —OQ₂,—S(O)_(z)Q₂, —S(O)_(z)N(Q₂)₂, —N(Q₂)₂, —C(O)OQ₂, —C(O)Q₂, —C(O)N(Q₂)₂,—C(O)N(Q₂)(OQ₂), —N(Q₂)C(O)Q₂, —N(Q₂)C(O)N(Q₂)₂, —N(Q₂)C(O)OQ₂,—N(Q₂)S(O)_(z)Q₂, or heterocycloalkyl or alkyl optionally substitutedwith 1-3 Q₃ substituents;

-   -   each Q₂ is independently hydrogen, alkyl, cycloalkyl, aryl,        arylalkyl, heterocycloalkyl, or heteroaryl, each optionally        substituted with 1-3 Q₃ substituents;    -   each Q₃ is independently halo, oxo, CN, NO₂, CF₃, OCF₃, OH,        —S(O)_(z)(C₁₋₆ alkyl), —N(C₁₋₆ alkyl)₂, —COO(C₁₋₆ alkyl), —C(O)        (C₁₋₆ alkyl), —O(C₁₋₆ alkyl), or a C₁₋₆ alkyl optionally        substituted with 1-3 substituents selected from halo, oxo, —CN,        —NO₂, —CF₃, —OCF₃, —OH, —SH, —S(O)_(z)H, —NH₂, or —COOH;    -   k is 0, 1, or 2; and    -   Y is an anion.

In some embodiments of Formulas Ia-Ie, each R, R′, and R″ isindependently alkyl or cycloalkyl, wherein each R, R′, and R″ isindependently and optionally substituted with halo, —CN, —NO₂, —OQ₂,—S(O)_(z)Q₂, —S(O)_(z)N(Q₂)₂, —N(Q₂)₂, —C(O)OQ₂, —C(O)Q₂, —C(O)N(Q₂)₂,—C(O)N(Q₂)(OQ₂), —N(Q₂)C(O)Q₂, —N(Q₂)C(O)N(Q₂)₂, —N(Q₂)C(O)OQ₂,—N(Q₂)S(O)_(z)Q₂, or heterocycloalkyl or alkyl optionally substitutedwith 1-3 Q₃ substituents. In another embodiment, each R, R′, and R″ isindependently alkyl or cycloalkyl, wherein each R, R′, and R″ isindependently and optionally substituted with halo, heterocycloalkyl,—CN, —NO₂, —OQ₂, —N(Q₂)₂, —C(O)OQ₂, —C(O)Q₂, or —C(O)N(Q₂)₂. In afurther embodiment, each R, R′, and R″ is independently alkyl, which isindependently and optionally substituted with halo, heterocycloalkyl,—CN, —NO₂, —OQ₂, —N(Q₂)₂, —C(O)OQ₂, —C(O)Q₂, or —C(O)N(Q₂)₂. In still afurther embodiment, each R, R′, and R″ is independently alkyl, which isindependently and optionally substituted with halo, heterocycloalkyl,—CN, —NO₂, —N(Q₂)₂, or —C(O)N(Q₂)₂.

In one embodiment, each R, R′, and R″ is independently an unsubstitutedalkyl. In another embodiment, each R, R′, and R″ is independentlyselected from methyl, ethyl, propyl, isopropyl, butyl, isobutyl,sec-butyl, tert-butyl, pentyl, hexyl, heptyl, 2-ethylhexyl, octyl,nonyl, decyl, dodecyl, and cetyl. In one embodiment, each R, R′, and R″is independently selected from methyl, ethyl, propyl, butyl, pentyl,hexyl, heptyl, octyl, nonyl, decyl, dodecyl, and cetyl.

In some embodiments of Formulas Ia-Ie, Y is selected from fluoride,chloride, bromide, iodide, arsenate, phosphate, arsenite, hydrogenphosphate, dihydrogen phosphate, sulfate, nitrate, hydrogen sulfate,nitrite, thiosulfate, sulfite, perchlorate, iodate, chlorate, bromate,chlorite, hypochlorite, hypobromite, carbonate, chromate, hydrogencarbonate (bicarbonate), dichromate, acetate, formate, cyanide, amide,cyanate, peroxide, thiocyanate, oxalate, hydroxide, and permanganate. Ina further embodiment, Y is a monovalent anion selected from fluoride,chloride, bromide, iodide, dihydrogen phosphate, nitrate, perchlorate,hypochlorite, hydrogen carbonate (bicarbonate), acetate, formate,cyanide, and hydroxide. In another further embodiment, Y is selectedfrom a bivalent anion selected from hydrogen phosphate, sulfate, andcarbonate. In still a further embodiment, Y is selected from fluoride,chloride, bromide and iodide. In one embodiment, Y is chloride. In oneembodiment, Y is bromide. In one embodiment, Y is iodide.

In some embodiments of Formulas Ia-Ie, k is 0 or 1. In a furtherembodiment, k is 0. In another further embodiment, k is 1.

In some embodiments of Formula Ia, each R and R′ is independentlyselected from methyl, ethyl, butyl, and hexyl. In a further embodiment,k is 1; R′ is selected from ethyl, butyl, and hexyl; and R is methyl. Inanother further embodiment, k is 0 and R′ is selected from ethyl, butyl,and hexyl.

In one embodiment, the salt of Formula Ia is selected from1-ethyl-3-methylpyridinium bromide, 1-ethyl-2-methylpyridinium bromide,1-butyl-3-methylpyridinium bromide, 1-butyl-4-methylpyridinium bromide,and 1-hexylpyridinium bromide.

In some embodiments of Formula Ib, each R, R′, and R″ is independentlyselected from methyl and propyl.

In one embodiment, the salt of Formula Ib is1-methyl-1-propylpiperidinium bromide.

In some embodiments of Formula Ic, each R, R′, and R″ is independentlyselected from methyl, ethyl, and butyl. In a further embodiment, k is 0.

In one embodiment, the salt of Formula Ic is selected fromN-methyl-N-ethylmorpholinium bromide and N-methyl-N-butylmorpholiniumbromide.

In some embodiments of Formula Id, each R, R′, and R″ is independentlyselected from methyl, ethyl, butyl, hexyl, octyl, and decyl. In afurther embodiment, k is 1 and R is methyl.

In one embodiment, the salt of Formula Id is selected from1-ethyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazoliumbromide, 1-ethyl-2,3-dimethylimidazolium bromide,1-decyl-3-methylimidazolium bromide, 1-butyl-2,3-dimethylimidazoliumbromide, 1-methyl-3-octylimidazolium bromide, and1-methyl-3-hexylimidazolium bromide.

In some embodiments of Formula Ie, each R, R′, and R″ is independentlyselected from methyl, ethyl, propyl, butyl, pentyl, and hexyl. Inanother embodiment, k is 0 and each R′ and R″ is independently an alkyl,which is optionally substituted by heterocycloalkyl or halo. In afurther embodiment, k is 0 and each R′ and R″ is independently selectedfrom methyl, ethyl, propyl, butyl, pentyl, hexyl, 2-choroethyl, or3-(N-methylpyrrolidinium)propyl.

In one embodiment, the salt of Formula Ie is selected fromN-methyl-N-ethylpyrrolidinium bromide, N-ethyl-N-propylpyrrolidiniumbromide, N-propyl-N-butylpyrrolidinium bromide,N-methyl-N-butylpyrolidinium bromide,N-ethyl-N-(2-chloroethyl)pyrrolidinium bromide,N-methyl-N-hexylpyrrolidinium bromide, N-methyl-N-pentylpyrrolidiniumbromide, N-ethyl-N-pentylpyrrolidinium bromide,N-ethyl-N-butylpyrrolidinium bromide, N-butyl-N-pentylpyrrolidiniumbromide, N-methyl-N-propylpyrrolidinium bromide,trimethylene-bis(N-methylpyrrolidinium) dibromide, andN-propyl-N-pentylpyrrolidinium bromide.

In some embodiments, the one or more quaternary ammonium agent comprisesan agent having the chemical formula

wherein R₁, R₂, R₃, and R₄ are each independently hydrogen or an alkylgroup, and Y is an anion as defined herein. In some embodiments, the oneor more quaternary ammonium agents comprises ammonium halides (e.g.,NH₄Br, NH₄Cl, or any combination thereof); tetra-alkylammonium halides(e.g., tetramethylammonium bromide, tetramethylammonium chloride,tetraethylammonium bromide, tetraethylammonium chloride, combinationsthereof, or the like); heterocyclic ammonium halides (e.g.,N-methyl-N-ethylpyrrolidinium halide, N-ethyl-N-methylpyrrolidiniumhalide, combinations thereof, or the like); or any combination thereof.In some embodiments, the one or more quaternary ammonium agentscomprises a quaternary ammonium agent selected from the group consistingof ammonium chloride, ammonium bromide, tetraethylammonium bromide,trimethylpropylammonium bromide, N-methyl-N-ethylmorpholinium bromide,N-ethyl-N-methylmorpholinium bromide, N-methyl-N-butylmorpholiniumbromide, N-methyl-N-ethylpyrrolidinium bromide,N,N,N-triethyl-N-propylammonium bromide, N-ethyl-N-propylpyrrolidiniumbromide, N-propyl-N-butylpyrrolidinium bromide,N-methyl-N-butylpyrolidinium bromide,N-ethyl-N-(2-chloroethyl)pyrrolidinium bromide,N-methyl-N-hexylpyrrolidinium bromide, N-methyl-N-pentylpyrrolidiniumbromide, N-ethyl-N-pentylpyrrolidinium bromide,N-ethyl-N-butylpyrrolidinium bromide,trimethylene-bis(N-methylpyrrolidinium) dibromide,N-butyl-N-pentylpyrrolidinium bromide, N-methyl-N-propylpyrrolidiniumbromide, N-propyl-N-pentylpyrrolidinium bromide, and any combinationthereof. In some examples, the electrolyte comprises from about 1 wt %to about 5 wt % of one or more quaternary ammonium agents. In someexamples, the electrolyte comprises from about 3 wt % to about 7 wt % ofone or more quaternary ammonium agents. And, in some embodiments, theone or more quaternary ammonium agents comprisesN-methyl-N-ethylmorpholinium bromide. In other examples, the electrolytecomprises from about 0.25 wt % to about 1.25 wt % ofN-methyl-N-ethylmorpholinium bromide. And, in some examples, the one ormore quaternary ammonium agents comprises tetraethylammonium bromide,trimethylpropylammonium bromide, or any combination thereof. Forinstance, the electrolyte comprises from about 1 wt % to about 5 wt % oftetraethylammonium bromide.

In some embodiments, the one or more quaternary ammonium agentscomprises a quaternary ammonium agent selected from the group consistingof an ammonium bromine complexing agent, an imidazolium brominecomplexing agent, a pyrrolidinium bromine complexing agent, a pyridiniumbromine complexing agent, a phosphonium bromine complexing agent, and amorpholinium bromine complexing agent.

In some embodiments, the one or more quaternary ammonium agentscomprises a quaternary ammonium agent selected from the group consistingof (TEA) tetraethylammonium bromide,(MEM)N-Ethyl-N-methylmorpholiniumbromide, trimethylpropylammoniumbromide, 1-ethyl-3-methylimidazolium bromide,1-butyl-3-methylimidazolium bromide, 1-butyl-1-methylpyrrolidiniumbromide, 1-ethyl-3-methylpyridinium bromide, 1-ethyl-3-methylpyridiniumbromide, 1-ethyl-2-methylpyridinium bromide,1-methyl-1-propylpiperidinium bromide, dodecyltrimethylammonium bromide,1-ethyl-2,3-dimethylimidazolium bromide, 1-decyl-3-methylimidazoliumbromide, 1-butyl-2,3-dimethylimidazolium bromide,1-methyl-3-octylimidazolium bromide, 1-methyl-3-hexylimidazoliumbromide, 1-butyl-3-methylpyridinium bromide, 1-butyl-4-methylpyridiniumbromide, 1-hexylpyridinium bromide, tetraethylphosphonium bromide,1-methyl-1-propylpyrrolidinium bromide, hexyltrimethylammonium bromide,and cetyltriethylammonium bromide.

In some embodiments, the one or more quaternary ammonium agentscomprises 1-ethyl-3-methylpyridinium bromide, 1-ethyl-2-methylpyridiniumbromide, 1-butyl-3-methyl pyridinium bromide, or 1-butyl-1-methylpyrrolidinium bromide. For example, the electrolyte comprises from about1 wt % to about 5 wt % (e.g., from about 1.5 wt % to about 4 wt %) of1-ethyl-3-methylpyridinium bromide, 1-ethyl-2-methylpyridinium bromide,1-butyl-3-methyl pyridinium bromide, 1-ethyl-1-methylmorpholiniumbromide, or 1-butyl-1-methyl pyrrolidinium bromide.

In some embodiments, the one or more quaternary ammonium agentscomprises cetyltriethylammonium bromide (CTAB). For example, theelectrolyte comprises from about 0.01 wt % to about 1 wt % (e.g., fromabout 0.05 wt % to about 0.5 wt %) of cetyltriethylammonium bromide(CTAB).

In some embodiments, the one or more quaternary ammonium agentscomprises tetraethylammonium bromide, trimethylpropylammonium bromide,or any combination thereof. For example, the electrolyte comprises fromabout 1 wt % to about 6 wt % (e.g., from about 1.5 wt % to about 5 wt %)of tetraethylammonium bromide. For example, the electrolyte comprisesfrom about 1 wt % to about 5 wt % (e.g., from about 1.5 wt % to about3.5 wt %) of trimethylpropylammonium bromide.

Without being bound by theory, it is thought that the quaternaryammonium agents enhance electrochemistry by creating a buoyancy effectwith the bromine complexes formed with the quaternary ammonium agents.As bromide ions in the electrolyte pseudo-polymerize, they becomeheavier and sink to the bottom of the electrolyte volume, reducingkinetics in the cell. Quaternary ammonium agents that create a buoyancyeffect help mitigate this issue, bringing the pseudo-polymerized bromideions off the bottom of the electrolyte volume, and increasing kineticsin the cell.

In some embodiments, the electrolyte further comprises less than 1 wt %of one or more additives selected from Sn, In, Ga, Al, Tl, Bi, Pb, Sb,Ag, Mn, Fe, or any combination thereof. For example, the electrolytecomprises less than 1 wt % of Sn and In.

In some embodiments, the electrolyte further comprises from about 30 wt% to about 50 wt % of water. In some embodiments, the electrolytefurther comprises from about 35 wt % to about 45 wt % of water. In someexamples, the water is de-mineralized until its resistance is greaterthan about 8 MΩ·cm (e.g., about 10 MΩ·cm or greater or greater thanabout 10 MΩ·cm).

In some embodiments, the electrolyte further comprises sufficient HBr toimpart the electrolyte with a pH of from about 2 to about 4 (from about2.5 to about 3.5).

In some embodiments, the electrolyte further comprises from about 0.1 wt% to about 2 wt % (e.g., from about 0.3 wt % to about 1 wt %) of aceticacid. In alternative embodiments, the electrolyte comprises from about0.1 wt % to about 2 wt % of acetic acid, sodium acetate, potassiumacetate, or any combination thereof.

In some embodiments, the electrolyte further comprises from about 2 wt %to about 8 wt % (e.g., from about 3 wt % to about 5 wt %) citric acidmonohydrate. In some embodiments, the electrolyte further comprises fromabout 2 wt % to about 8 wt % (e.g., from about 3 wt % to about 5 wt %)of potassium dihydrogen citrate monohydrate.

In some embodiments, the electrolyte further comprises from about 2 wt %to about 8 wt % (e.g., from about 3 wt % to about 5 wt %) oxalic acid.In some embodiments, the electrolyte further comprises from about 2 wt %to about 8 wt % (e.g., from about 3 wt % to about 5 wt %) of oxalicacid.

In some embodiments the electrolyte further comprises a stable additive.For example, the stable additive is acetic acid, sodium acetate, oxalicacid, sodium oxalate, citric acid, potassium citrate, 18-crown-6,dicyandiamide, succinic acid, sodium methane sulfonate, sodiumproprionate, sodium malonate, sodium hexanoate, sodiumhexafluoroaluminate, sebacic acid, potassium trifluoromethanesulfonate,acetonitrile, propionitrile, acquivion ionomer, sodium butyrate,melamine, sebaic acid, 2,2 bipyridine, dodecanedioic acid, sodiumtrichloroacetate, dodecanoic acid, sodium dodecanoate, 15-crown-5, ortrichloroacetic acid. In some embodiments the additives enhanceelectrochemistry. In other embodiments the additives do not change theelectrochemistry.

Another aspect of the present invention provides an electrolyte for usein a secondary zinc halide electrochemical cell comprising from about 30wt % to about 40 wt % of ZnBr₂, ZnCl₂, or any combination thereof; fromabout 4 wt % to about 12 wt % of KBr; from about 4 wt % to about 12 wt %of KCl; from about 0.5 wt % to about 10 wt % of a glyme; and from about1 wt % to about 5 wt % of one or more quaternary ammonium agents.

Another aspect of the present invention provides an electrolyte for usein a secondary zinc halide electrochemical cell comprising from about 30wt % to about 40 wt % of ZnBr₂; from about 4 wt % to about 12 wt % ofKBr; from about 4 wt % to about 12 wt % of KCl; from about 0.5 wt % toabout 10 wt % of a glyme; and from about 1 wt % to about 5 wt % of oneor more quaternary ammonium agents.

Another aspect of the present invention provides an electrolyte for usein a secondary zinc halide electrochemical cell comprising from about 30wt % to about 40 wt % of ZnBr₂ and from about 0.01 wt % to about 0.9 wt% of one or more additives selected from Sn, In, Ga, Al, Tl, Bi, Pb, Sb,Ag, Mn, Fe, or any combination thereof.

In some embodiments, the electrolyte comprises from about 30 wt % toabout 40 wt % of ZnBr₂; from about 5 wt % to about 15 wt % of KBr; fromabout 5 wt % to about 15 wt % of KCl; from about 0.5 wt % to about 10 wt% of one or more quaternary ammonium agents; from about 0.1 wt % toabout 2 wt % of acetic acid; and from about 0.05 wt % to about 4 wt % ofa crown ether.

In some embodiments, the electrolyte comprises from about 30 wt % toabout 40 wt % of ZnBr₂; from about 5 wt % to about 15 wt % of KBr; fromabout 5 wt % to about 15 wt % of KCl; from about 0.5 wt % to about 10 wt% of one or more quaternary ammonium agents; from about 0.1 wt % toabout 2 wt % of acetic acid; from about 0.05 wt % to about 4 wt % of acrown ether; and wherein the one or more quaternary ammonium agentscomprises tetraethylammonium bromide.

In some embodiments, the electrolyte comprises from about 30 wt % toabout 40 wt % of ZnBr₂; from about 5 wt % to about 15 wt % of KBr; fromabout 5 wt % to about 15 wt % of KCl; from about 0.5 wt % to about 10 wt% of one or more quaternary ammonium agents; from about 0.1 wt % toabout 2 wt % of acetic acid; from about 0.05 wt % to about 4 wt % of acrown ether; and wherein the one or more quaternary ammonium agentscomprises trimethylpropylammonium bromide.

In some embodiments, the electrolyte comprises from about 30 wt % toabout 40 wt % of ZnBr₂; from about 5 wt % to about 15 wt % of KBr; fromabout 5 wt % to about 15 wt % of KCl; from about 0.5 wt % to about 10 wt% of one or more quaternary ammonium agents; from about 0.1 wt % toabout 2 wt % of acetic acid; from about 0.05 wt % to about 4 wt % of acrown ether; and wherein the one or more quaternary ammonium agentscomprises tetraethylammonium bromide, methylethylpyridinium bromide, andcetyltriethylammonium bromide. In a further embodiment, themethylethylpyridinium bromide is 1-ethyl-2-methylpyridinium bromide. Ina further embodiment, the methylethylpyridinium bromide is1-ethyl-3-methylpyridinium bromide.

In some embodiments, the electrolyte comprises from about 30 wt % toabout 40 wt % of ZnBr₂; from about 5 wt % to about 15 wt % of KBr; fromabout 5 wt % to about 15 wt % of KCl; from about 0.5 wt % to about 10 wt% of one or more quaternary ammonium agents; from about 0.1 wt % toabout 2 wt % of acetic acid; from about 0.05 wt % to about 4 wt % of acrown ether; and wherein the one or more quaternary ammonium agentscomprises triethylpropylammonium bromide, methylethylpyridinium bromide,and cetyltriethylammonium bromide. In a further embodiment, themethylethylpyridinium bromide is 1-ethyl-2-methylpyridinium bromide.

In some embodiments, the electrolyte comprises from about 30 wt % toabout 40 wt % of ZnBr₂; from about 5 wt % to about 15 wt % of KBr; fromabout 5 wt % to about 15 wt % of KCl; from about 0.5 wt % to about 10 wt% of one or more quaternary ammonium agents; from about 0.1 wt % toabout 2 wt % of acetic acid; from about 0.05 wt % to about 4 wt % of acrown ether; and wherein the one or more quaternary ammonium agentscomprises triethylpropylammonium bromide, 1-butyl-3-methylpyridiniumbromide, and cetyltriethylammonium bromide.

In some embodiments, the electrolyte comprises from about 30 wt % toabout 40 wt % of ZnBr₂; from about 5 wt % to about 15 wt % of KBr; fromabout 5 wt % to about 15 wt % of KCl; from about 0.5 wt % to about 10 wt% of one or more quaternary ammonium agents; from about 0.1 wt % toabout 2 wt % of acetic acid; from about 0.05 wt % to about 4 wt % of acrown ether; and wherein the one or more quaternary ammonium agentscomprises tetraethylammonium bromide, 1-butyl-3-methylpyridiniumbromide, and cetyltriethylammonium bromide.

In some embodiments, the electrolyte comprises from about 30 wt % toabout 40 wt % of ZnBr₂; from about 5 wt % to about 15 wt % of KBr; fromabout 5 wt % to about 15 wt % of KCl; from about 0.5 wt % to about 10 wt% of one or more quaternary ammonium agents; from about 0.1 wt % toabout 2 wt % of acetic acid; from about 0.05 wt % to about 4 wt % of acrown ether; and wherein the one or more quaternary ammonium agentscomprises tetraethylammonium bromide, 1-ethyl-1-methylmorpholiniumbromide, and cetyltriethylammonium bromide.

In some embodiments. the electrolyte comprises from about 30 wt % toabout 40 wt % of ZnBr₂; from about 5 wt % to about 15 wt % of KBr; fromabout 5 wt % to about 15 wt % of KCl; from about 0.5 wt % to about 10 wt% of one or more quaternary ammonium agents; from about 0.1 wt % toabout 2 wt % of acetic acid; from about 0.05 wt % to about 4 wt % of acrown ether; and wherein the one or more quaternary ammonium agentscomprises trimethylpropylammonium bromide, 1-butyl-1-methylpyrrolidiniumbromide, and cetyltriethylammonium bromide.

In some embodiments, the electrolyte comprises from about 30 wt % toabout 40 wt % of ZnBr₂; from about 5 wt % to about 15 wt % of KBr; fromabout 5 wt % to about 15 wt % of KCl; from about 0.5 wt % to about 10 wt% of one or more quaternary ammonium agents; wherein the one or morequaternary ammonium agents comprises tetraethylammonium bromide,methylethylpyridinium bromide, and cetyltriethylammonium bromide.

In some embodiments, the electrolyte comprises from about 30 wt % toabout 40 wt % of ZnBr₂; from about 5 wt % to about 15 wt % of KBr; fromabout 5 wt % to about 15 wt % of KCl; from about 0.5 wt % to about 10 wt% of one or more quaternary ammonium agents; wherein the one or morequaternary ammonium agents comprises trimethylpropylammonium bromide,1-butyl-1-methylpyrrolidinium bromide, and cetyltriethylammoniumbromide.

Methods of Preparing an Electrolyte

Another aspect of the present invention provides a method of preparingan electrolyte for use in a secondary zinc halide electrochemical cellcomprising mixing ZnBr₂, KBr, KCl; water, and one or more quaternaryammonium agents to generate a mixture, wherein the mixture comprisesfrom about 30 wt % to about 40 wt % of ZnBr₂; from about 4 wt % to about12 wt % of KBr; from about 4 wt % to about 12 wt % of KCl; from about0.5 wt % to about 10 wt % of the one or more quaternary ammonium agents;and from about 25 wt % to about 45 wt % of water.

Alternatively, the mixture comprises from about 30 wt % to about 40 wt %of ZnBr₂; from about 8 wt % to about 12 wt % of KBr; from about 8 wt %to about 14 wt % of KCl; from about 0.5 wt % to about 10 wt % of the oneor more quaternary ammonium agents; and from about 25 wt % to about 45wt % of water.

In some implementations, the mixture comprises from about 32 wt % toabout 36 wt % of ZnBr₂.

In some implementations, the mixture comprises from about 4 wt % toabout 12 wt % (e.g., from about 6 wt % to about 10 wt %) of potassiumbromide (KBr). In some implementations, the mixture comprises from about8 wt % to about 12 wt % of potassium bromide (KBr).

In some implementations, the mixture comprises from about 4 wt % toabout 12 wt % (e.g., from about 6 wt % to about 10 wt %) of potassiumchloride (KCl). In some implementations, the mixture comprises fromabout 8 wt % to about 14 wt % of potassium chloride (KCl). In someimplementations, the mixture comprises from about 11 wt % to about 14 wt% of potassium chloride (KCl).

In some implementations, the mixture comprises from about 27 wt % toabout 43 wt % (e.g., from about 30 wt % to about 40 wt % or from about35 wt % to about 41 wt %) of water.

In some implementations, the one or more quaternary ammonium agents is asalt of Formula I

as described herein.

In some implementations, the one or more quaternary ammonium comprises aquaternary ammonium agent selected from the group consisting of anammonium halide (e.g., NH₄Br, NH₄Cl, or any combination thereof); atetra-alkylammonium halide (e.g., tetramethylammonium bromide,tetramethylammonium chloride, tetraethylammonium bromide,tetraethylammonium chloride, combinations thereof or the like); aheterocyclic ammonium halides (e.g., N-methyl-N-ethylpyrrolidiniumhalide, N-ethyl-N-methylpyrrolidinium halide, combinations thereof, orthe like); or any combination thereof. In other implementations, the oneor more quaternary ammonium agents comprises a quaternary ammonium agentselected from the group consisting of ammonium chloride,tetraethylammonium bromide, trimethylpropylammonium bromide,N-methyl-N-ethylmorpholinium bromide, N-ethyl-N-methylmorpholiniumbromide, N-methyl-N-butylmorpholinium bromide,N-methyl-N-ethylpyrrolidinium bromide, N,N,N-triethyl-N-propylammoniumbromide, N-ethyl-N-propylpyrrolidinium bromide,N-propyl-N-butylpyrrolidinium bromide, N-methyl-N-butylpyrolidiniumbromide, N-ethyl-N-(2-chloroethyl)pyrrolidinium bromide,N-methyl-N-hexylpyrrolidinium bromide, N-methyl-N-pentylpyrrolidiniumbromide, N-ethyl-N-pentylpyrrolidinium bromide,N-ethyl-N-butylpyrrolidinium bromide,trimethylene-bis(N-methylpyrrolidinium) dibromide,N-butyl-N-pentylpyrrolidinium bromide, N-methyl-N-propylpyrrolidiniumbromide, N-propyl-N-pentylpyrrolidinium bromide, and any combinationthereof. In some examples, the mixture comprises from about 1 wt % toabout 5 wt % of one or more quaternary ammonium agents. And, in someimplementations, the one or more quaternary ammonium agents comprisesN-methyl-N-ethylmorpholinium bromide. In other examples, the mixturecomprises from about 0.25 wt % to about 1.25 wt % ofN-methyl-N-ethylmorpholinium bromide. And, in some examples, the one ormore quaternary ammonium agents comprises tetraethylammonium bromide,trimethylpropylammonium bromide, or any combination thereof. Forinstance, the electrolyte comprises from about 1 wt % to about 5 wt % oftetraethylammonium bromide.

In some implementations, the one or more quaternary ammonium agentscomprises a quaternary ammonium agent selected from the group consistingof an ammonium bromine complexing agent, an imidazolium brominecomplexing agent, a pyrrolidinium bromine complexing agent, a pyridiniumbromine complexing agent, a phosphonium bromine complexing agent, and amorpholinium bromine complexing agent.

In some implementations, the one or more quaternary ammonium agentscomprises a quaternary ammonium agent selected from the group consistingof (TEA) tetraethylammonium bromide,(MEM)N-Ethyl-N-methylmorpholiniumbromide, trimethylpropylammoniumbromide, 1-ethyl-3-methylimidazolium bromide,1-butyl-3-methylimidazolium bromide, 1-butyl-1-methylpyrrolidiniumbromide, 1-ethyl-3-methylpyridinium bromide, 1-ethyl-3-methylpyridiniumbromide, 1-ethyl-2-methylpyridinium bromide,1-methyl-1-propylpiperidinium bromide, dodecyltrimethylammonium bromide,1-ethyl-2,3-dimethylimidazolium bromide, 1-decyl-3-methylimidazoliumbromide, 1-butyl-2,3-dimethylimidazolium bromide,1-methyl-3-octylimidazolium bromide, 1-methyl-3-hexylimidazoliumbromide, 1-butyl-3-methylpyridinium bromide, 1-butyl-4-methylpyridiniumbromide, 1-hexylpyridinium bromide, tetraethylphosphonium bromide,1-methyl-1-propylpyrrolidinium bromide, hexyltrimethylammonium bromide,and cetyltriethylammonium bromide. For example, the one or morequaternary ammonium agents comprises 1-ethyl-3-methylpyridinium bromide,1-ethyl-2-methylpyridinium bromide, 1-butyl-3-methyl pyridinium bromide,or 1-butyl-1-methyl pyrrolidinium bromide. For example, the electrolytecomprises from about 1 wt % to about 4 wt % (e.g., from about 1.5 wt %to about 3 wt %) of 1-ethyl-3-methylpyridinium bromide,1-ethyl-2-methylpyridinium bromide, 1-butyl-3-methyl pyridinium bromide,or 1-butyl-1-methyl pyrrolidinium bromide.

In some embodiments, the one or more quaternary ammonium agentscomprises cetyltriethylammonium bromide (CTAB). For example, theelectrolyte comprises from about 0.05 wt % to about 1 wt % (e.g., fromabout 0.1 wt % to about 0.5 wt %) of cetyltriethylammonium bromide(CTAB).

In some embodiments, the one or more quaternary ammonium agentscomprises tetraethylammonium bromide, trimethylpropylammonium bromide,or any combination thereof. For example, the electrolyte comprises fromabout 1 wt % to about 5 wt % (e.g., from about 1.5 wt % to about 3.5 wt%) of tetraethylammonium bromide. For example, the electrolyte comprisesfrom about 1 wt % to about 5 wt % (e.g., from about 1.5 wt % to about3.5 wt %) of trimethylpropylammonium bromide.

Some implementations additionally comprise mixing a glyme with ZnBr₂ andother ingredients (e.g., KBr, KCl, quaternary ammonium agent, andwater), wherein the mixture comprises from about 0.5 wt % to about 10 wt% (e.g., from about 1 wt % to about 7.5 wt %) of a glyme. In someexamples, the glyme comprises monoglyme, diglyme, triglyme, tetraglyme,or any combination thereof. For instance, the glyme comprisestetraglyme. In other examples, the mixture comprises from about 1 wt %to about 5 wt % of tetraglyme.

Some implementations additionally comprise mixing DME-PEG with ZnBr₂ andother ingredients (e.g., KBr, KCl, quaternary ammonium agent, water,and/or glyme) to generate the mixture, wherein the mixture comprisesfrom about 0.5 wt % to about 2.5 wt % (e.g., from about 1 wt % to about2.25 wt %) of mPEG. In some examples, the DME-PEG has an averagemolecular weight (e.g., a number average molecular weight M_(n)) of fromabout 350 amu to about 3000 amu. In other examples, the DME-PEG has anaverage molecular weight (e.g., a number average molecular weight M_(n))of from about 1200 amu to about 3000 amu. And, in some examples, themixture further comprises from about 5 wt % to about 10 wt % of DME-PEG,wherein the DME-PEG has an average molecular weight (e.g., a numberaverage molecular weight M_(n)) of from about 1500 amu to about 2500 amu(e.g., about 2000 amu).

Some implementations additionally comprise mixing a crown ether withZnBr₂ and other ingredients (e.g., KBr, KCl, quaternary ammonium agent,water, etc.) to generate the mixture, wherein the mixture comprises fromabout 0.05 wt % to about 4 wt % of the crown ether. In some examples thecrown ether is 18-crown-6 or 15-crown-5. In some examples the mixturecomprises from about 0.1 wt % to about 1 wt % of the crown ether.

Some implementations additionally comprise mixing an alcohol that issubstantially miscible in water with ZnBr₂ and other ingredients (e.g.,KBr, KCl, quaternary ammonium agent, water, glyme, and/or DME-PEG) togenerate the mixture, wherein the mixture comprises from about 0.1 wt %to about 1.0 wt % of the alcohol. For example, the alcohol comprises aC₁₋₄ alcohol. In other examples, the alcohol comprises methanol,ethanol, 1-propanol, iso-propanol, 1-butanol, sec-butanol, iso-butanol,tert-butanol, or any combination thereof. And in some examples, themixture further comprises from about 0.25 wt % to about 0.75 wt % oftert-butanol.

Some implementations additionally comprise mixing a C₁₋₁₀ glycol withZnBr₂ and other ingredients (e.g., KBr, KCl, quaternary ammonium agent,water, glyme, DME-PEG, and/or alcohol) to generate the mixture, whereinthe mixture comprises from about 0.25 wt % to about 5 wt % (e.g., fromabout 0.5 wt % to about 4 wt %) of the C₁₋₁₀ glycol. In some examples,the glycol comprises ethylene glycol, propylene glycol, 1,3-butyleneglycol, 1,4-butylene glycol, neopentyl glycol, hexalene glycol, or anycombination thereof. And, in some examples, the mixture furthercomprises from about 0.25 wt % to about 2.5 wt % of neopentyl glycol.

Some implementations additionally comprise mixing one or more additivesselected from Sn, In, Ga, Al, Tl, Bi, Pb, Sb, Ag, Mn, or Fe with ZnBr₂and other ingredients (e.g., KBr, KCl, quaternary ammonium agent, water,glyme, DME-PEG, alcohol, and/or C₁₋₁₀ glycol), wherein the mixturecomprises less than 1 wt % of the one or more additives selected fromSn, In, Ga, Al, Tl, Bi, Pb, Sb, Ag, Mn, or Fe. For example, the mixturecomprises less than 1 wt % of Sn and In.

Some implementations additionally comprise adding a sufficient amount ofHBr to the mixture to impart the mixture with a pH of from about 2 toabout 4 (from about 2.5 to about 3.5).

Some implementations additionally comprise mixing acetic acid with ZnBr₂and other ingredients (e.g., KBr, KCl, quaternary ammonium agent, water,etc.) to generate the mixture, wherein the mixture comprises from about0.1 wt % to about 2 wt % (e.g., from about 0.3 wt % to about 1 wt %) ofacetic acid.

Some implementations additionally comprise mixing citric acidmonohydrate with ZnBr₂ and other ingredients (e.g., KBr, KCl, quaternaryammonium agent, water, etc.) to generate the mixture, wherein themixture comprises from about 2 wt % to about 8 wt % (e.g., from about 3wt % to about 5 wt %) citric acid monohydrate.

Some implementations additionally comprise mixing potassium dihydrogencitrate monohydrate with ZnBr₂ and other ingredients (e.g., KBr, KCl,quaternary ammonium agent, water, etc.) to generate the mixture, whereinthe mixture comprises from about 2 wt % to about 8 wt % (e.g., fromabout 3 wt % to about 5 wt %) of potassium dihydrogen citratemonohydrate.

In some implementations, the ZnBr₂, KBr, KCl, water, and one or morequaternary ammonium agents are mixed at a temperature of from about 15°C. to about 30° C. (e.g., room temperature).

In some implementations, the ZnBr₂, KBr, KCl; water, and one or morequaternary ammonium agents are mixed under agitation (e.g., the mixtureis stirred).

In some implementations, the mixtures described herein are optionallyfiltered. In some implementations, the mixtures described herein arefiltered. In some implementations, the mixtures described herein are notfiltered.

B. Battery Stacks

Referring to FIGS. 18-20, another aspect of the present inventionprovides a battery stack comprising a plurality of bipolar electrodes atleast partially disposed in zinc-halide electrolyte and interposedbetween a cathode terminal assembly and an anode terminal assembly. Thecathode terminal assembly, the anode terminal assembly, the zinc-halideelectrolyte, and the bipolar electrodes include any embodimentsdescribed herein.

1. Frame Members

In some embodiments, the battery stack or electrochemical cell of thepresent invention comprises a frame member 114 that is interposedbetween two adjacent bipolar electrodes or interposed between a bipolarelectrode and a terminal assembly (e.g., a terminal anode assembly or aterminal cathode assembly).

In one embodiment, illustrated in FIG. 23, the frame member has an outerperiphery edge 604, and an inner periphery edge 608 defining an openinterior region 606. The inner periphery edge 608 defines the openinterior region such that a cathode assembly of a bipolar electrode isimmediately adjacent to an inner surface of a terminal endplate or aback surface of an adjacent bipolar electrode plate without interferenceor obstruction from the frame member. Thus, the open interior region isat least as large as the electrochemically active area of a terminalendplate and at least as large as a reduced surface of a pocket portionof a cathode cage of a cathode assembly. In some embodiments, the framemember is configured such that open interior region is approximatelycentered about the center of an electrochemically active region of aterminal endplate received by the frame member and/or the center of acathode assembly disposed on a bipolar electrode plate of a bipolarelectrode. In some embodiments, the outer periphery of the frame memberdefines the outer surface of a battery stack or electrochemical cell.

In some embodiments, the frame member includes a first side 614 thatopposes and retains the first bipolar electrode plate or terminalendplate and a second side 616 disposed on an opposite side of the framemember than the first side that opposes and retains a second bipolarelectrode plate. The first and second electrode plates and the terminalendplate(s) may be configured to have substantially the same size andshape.

In some embodiments, each side of the frame member includes a sealinggroove 612 that extends around the inner periphery edge. In someexamples, each sealing groove is sized and shaped to conform to thecontour of the peripheral edge of the corresponding bipolar electrodeplate or terminal endplate retained by the frame member. And, in someembodiments, each sealing groove is configured to receive a seal 116(FIG. 21) (e.g., an o-ring or gasket) seated therein that forms asubstantially leak-free seal when the seal is compressed between thecorresponding electrode plate or endplate and the frame member when theelectrochemical cell or battery stack is assembled to provide a sealinginterface between the electrode plate or endplate and the frame member.The seals cooperate to retain the electrolyte between the opposingelectrode plates and a frame member, or between an electrode plate, anendplate and a frame member.

In some embodiments, the frame member has one or more retaining fences610 that protrude into the open interior region and restrain acompression plate 105 or electrode plate from movement when the batteryis assembled. In other embodiments, one or more retaining fences mayextend into the interior region from the inner periphery edge. In someexamples, the retaining fences are operative to contact a substantiallyflat surface of the cathode cage (e.g., the pocket portion of thecathode cage) that protrudes away from the front surface of an electrodeplate in a direction toward the frame member. The retaining fence mayreduce or prevent the bending and deforming of the cathode cage fromflat during charging of the battery module. The retaining fences mayinclude openings or cut outs to reduce overall weight of the framemember.

Each frame member may be formed from flame retardant polypropylenefibers. Each frame member may receive two adjacent electrode plates oran electrode plate and a terminal endplate. And, one of the electrodeplates may include a surface joined to a cathode assembly having acarbon material and a separator arranged in a layered configuration anda cathode cage enclosing the carbon material and the separator. Eachframe may also house an aqueous electrolyte solution (e.g., zinc-halideelectrolyte or zinc-bromide electrolyte). As illustrated in FIG. 19, aframe member disposed adjacent to a compression plate may optionallyinclude one or more pressure release valves to release excess pressurefrom within the electrochemical cell or battery stack. In someembodiments, the pressure relief valve includes a molded carrierconfigured to extend through the frame and a pressure relief umbrella.

2. Compression Plates

In some embodiments, the electrochemical cell or battery stack comprisesa pair of compression plates 105, 105 a, 105 b located at the ends ofthe electrochemical cell or battery stack. In some embodiments, eachcompression plate includes an exterior surface 512 and an interiorsurface 504 disposed on an opposite side of the compression plate thanthe exterior surface and opposing an adjacent frame member. FIG. 22shows the exterior surface of the compression plate associated with thepositive (+) anode terminal of the electrochemical cell or battery stackand the interior surface of the compression plate associated with thenegative (−) cathode of the electrochemical cell or battery stack. Insome embodiments, the compression plates are formed from 6061-T6aluminum and may be manufactured by stamping. In other embodiments, thecompression plates are formed of stainless steel and may be manufacturedby machining.

In some embodiments, a terminal hole 502 a, 502 b extends through eachcompression plate to expose a corresponding terminal for electricalconnection with a connection/power cable. In some embodiments, thecompression plates have thru holes formed through the compression platesthat are operative to receive one or more frame bolts or tie rods 120.For example, a first row of four (4) thru holes may be spaced apart(e.g., evenly spaced apart) along the top edge of each compression plateand a second row of four (4) thru holes may be spaced apart (e.g.,evenly spaced apart) along the bottom edge of each compression plate.

The outer surface of each compression plate may include cut-outs 508 toreduce weight of the compression plates and to define reinforcementmembers that reduce stress concentration when the compression platecontacts adjacent terminal frame members. Moreover, the cut-outs maydissipate heat that the electrochemical cell or battery stack generates.The exterior surface and the cut-outs may define one or more channels510 operative to receive and route the connection/power cables thatelectrically connect with the exposed terminals and/or a wiring harnessfor the assembled battery module. And, in some embodiments, eachinterior surface of the compression plate has one or more cut-outs.

In some embodiments, the interior surface of each compression plate mayinclude a substantially flat surface operative to engage an outersurface of an adjacent frame member. In some embodiments, the interiorsurface of each compression plate also defines a recessed area having asize and shape configured to receive at least a portion of a conductivecup-shaped member joined to and protruding from the terminal endplateassociated with the corresponding adjacent compression plate. In someembodiments, an aperture may extend through the interior and exteriorsurfaces of the compression plate endplate in place of the recessed areato expose at least a portion of a conductive-cup shaped member andterminal.

In some embodiments of electrochemical cells or battery stacks of thepresent invention, each frame member and each pair of compression plateshave corresponding thru holes that are configured to receive bolts ortie rods therethrough and operate to compress these components usingfasteners (e.g., nuts 108 and/or washers 106, 110) to assemble asubstantially sealed electrochemical cell or battery stack.

In some embodiments, each frame member, each compression plate, eachterminal endplate, and each bipolar electrode plate has one or morecorresponding thru holes that operate to align the components such thatthe terminal, the conductive cup-shaped member, the cathode assembly,and the electrochemically active region share the same approximatecenter when dowels 112 are placed therethough.

In some embodiments, the battery stack comprises a first bipolarelectrode, a second bipolar electrode, and a frame member 114, whereinthe frame member is interposed between the first bipolar electrode, theframe member has a first side and a second side, the first bipolarelectrode has a first electrode plate, and the second bipolar electrodehas a second bipolar plate; and wherein the first side of the framemember is configured to receive at least a portion of a front side ofthe first electrode plate, and the second side of the frame member isconfigured to receive at least a portion of a back side of the secondelectrode plate.

Referring to FIGS. 19 and 20, another aspect of the present inventionprovides a bipolar battery stack defining a longitudinal axis L, thebipolar battery 1000 comprising a pair of terminal assemblies 104 atcorresponding proximal and distal ends of the battery, each terminalassembly comprising a conductive cup-shaped member 310 comprising aterminal wall 312, a sidewall 304, and a rim 306 separated from theterminal wall by the sidewall; and a terminal endplate 302 having outerand inner surfaces 316, 318 coplanar with the terminal wall and joiningto the corresponding rim at the outward surface, the joining enablingbi-directional uniform current flow through the cup-shaped memberbetween a corresponding terminal 308 and the endplate when thecorresponding terminal wall is in electrical contact with thecorresponding terminal. In some embodiments, the terminal assemblycorresponds to the terminal assembly 104 described above with referenceto FIGS. 12-17. In some embodiments, the battery stack 1000 furthercomprises at least one pair of intermediate bipolar electrodes 102, 102′arranged in a parallel orientation between the pair of terminalassemblies. In these embodiments, the intermediate cells comprisebipolar electrodes for distributing current between the terminalassemblies. Each intermediate cell comprises a frame member 114 thathouses components of the cell.

FIG. 20 provides an exploded view of the battery stack of FIG. 19. Insome embodiments, each battery stack or electrochemical cell furthercomprises corresponding compression plates 105 a, 105 b opposed to andreleasably fastened in contact with the outer surfaces of the endplates302, each compression plate comprising an aperture 502 a, 502 bconfigured to receive the corresponding terminal 308. In some of theseembodiments, at least a portion of the terminal wall of the conductivecup-shaped member is exposed through the aperture of the compressionplate. In other embodiments, the terminal wall and at least a portion ofthe sidewall is exposed through the aperture of the compression plates.FIG. 7 illustrates the compression plates having their correspondingapertures formed therethrough. In other embodiments, a recessed area maybe disposed at the inward surface of each compression plate that isconfigured to receive the corresponding cup-shaped member. In theseembodiments, a terminal hole may be formed through the recessed area ofeach compression plate to expose the terminal. In some embodiments,outward/exterior surfaces of the compression plates include cut-outs toreduce the overall weight of the compression plates and to helpdissipate heat generated by the battery.

In some embodiments, the compression plates include openings operativeto receive tie rods and/or bolts secured by fasteners to compress thetwo compression plates and intervening frame members together alonglongitudinal axis L (FIG. 19) when the battery stack is assembled.

In some embodiments, an electrochemically active region of eachcorresponding terminal endplate comprises a first surface area enclosedby the corresponding rim and a remaining second surface area outside anouter periphery of the corresponding rim, the first and second surfaceareas being substantially equal.

In some embodiments, each terminal wall projects away from the outwardsurface of the corresponding endplate.

In some embodiments, one of the terminal walls projects away from theoutward surface of the corresponding endplate in a proximal directionalong the longitudinal axis and the other terminal wall projects awayfrom the outward surface of the corresponding endplate in an oppositedistal direction along the longitudinal axis.

In some embodiments, the terminal walls of the conductive cup-shapedmembers are exposed at corresponding ones of the proximal and distalends of the electrochemical cell assembly.

In some embodiments, one of the terminal assemblies in the battery stackor electrochemical cells further comprises a cathode assembly 202disposed on an inner surface of the corresponding endplate on a sideopposite the corresponding conductive cup-shaped member, the cathodeassembly interposed between the inner surface of the endplate and a backsurface of an adjacent bipolar electrode plate.

In some embodiments, each rim is centered within the electrochemicallyactive region of the corresponding endplate.

In some embodiments, each rim of the conductive cup-shaped members isjoined to the outward surface of the corresponding endplate by a weld oran adhesive. In some instances, the adhesive is electrically conductive.

In some embodiments, at least one of the conductive cup-shaped memberscomprises a copper/titanium clad.

In some embodiments, interior surfaces of at least one of the conductivecup-shaped members comprises copper. In other embodiments, exteriorsurfaces of at least one of the conductive cup-shaped members comprisestitanium.

In some embodiments, each corresponding terminal contacts a centrallocation of the corresponding terminal wall.

In some embodiments, the rim comprises a flange extending radiallyoutward from the sidewall.

IV. Examples Example 1A—Electrolyte Formulations

Ingredients used in the electrolyte formulations described below werereagent grade.

TABLE 1 Ingredients for electrolyte ingredients Ingredient Source ZnBr₂(73-79% ZnBr₂ soln. in water) ICL IP America, Inc., Carteret, NJ KBrAlfa Aesar, Ward Hill, MA KCl Alfa Aesar, Ward Hill, MA tetraglyme SigmaAldrich Corp., St. Louis, MO DME-PEG 2000 Sigma Aldrich Corp., St.Louis, MO DME-PEG 1000 Alfa Aesar, Ward Hill, MAN-methyl-n-ethylmorpholinium bromide ICL-IP Bromine Compounds, Ltd.,Beer-Sheva, Israel neopentyl glycol Sigma Aldrich Corp., St. Louis, MOtert-butyl alcohol Alfa Aesar, Ward Hill, MA Sn (SnCl₂•2H₂O) Alfa Aesar,Ward Hill, MA In (5% v/v in dilute nitric acid - 10,050 μg/ml) InorganicVentures, Christiansburg, VA acetic acid (glacial) Alfa Aesar, WardHill, MA 18-crown-6 ether Sigma Aldrich Corp., St. Louis, MO 15-crown-5ether Sigma Aldrich Corp., St. Louis, MO tetraethylammonium bromide AlfaAesar, Ward Hill, MA 1-ethyl-2-methylpyridinium bromide ICL-IP BromineCompounds, Ltd., Beer-Sheva, Israel 1-ethyl-1-methylmorpholinium bromideICL-IP Bromine Compounds, Ltd., Beer-Sheva, Israelcetyltrimethylammonium bromide Amresco, Solon, OH1-butyl-1-methylpyrrolidinium bromide ICL-IP Bromine Compounds, Ltd.,Beer-Sheva, Israel 1-butyl-3-methylpyridinium bromide ICL-IP BromineCompounds, Ltd., Beer-Sheva, Israel trimethylpropylammonium bromideICL-IP Bromine Compounds, Ltd., Beer-Sheva, Israel potassium dihydrogencitrate monohydrate Sigma Aldrich Corp., St. Louis, MO citric acidmonohydrate Sigma Aldrich Corp., St. Louis, MO HBr (48 wt % in H₂O)Sigma Aldrich Corp., St. Louis, MO proprionic acid (99.5%≦) SigmaAldrich Corp., St. Louis, MO tetraethylphosphonium bromide (99%≦) SigmaAldrich Corp., St. Louis, MO triethyl-N-methoxymethylammonium bromideHangzhou Yanshan Chemical Co., Ltd. trimethylproplyammonium bromideSigma Aldrich Corp., St. Louis, MO triethylmethylammonium bromide SigmaAldrich Corp., St. Louis, MO hexyltrimethylammonium bromide SigmaAldrich Corp., St. Louis, MO chloroethylammonium chloride Sigma AldrichCorp., St. Louis, MO

Electrolytes of the present invention was formulated as follows:

TABLE 2 Electrolyte no. 1-1 formulation (base formulation). IngredientAmount (g) Wt % ZnBr₂ 85 36.31 water 95 40.58 KBr 21 8.97 KCl 20 8.54Acetic acid 1.11 0.47 1-ethyl-2-methylpyridinium bromide 4.96 2.12tetraethylammonium bromide 6.1 2.61 18-crown-6 0.55 0.23cetyltrimethylammonium bromide 0.4 0.17 Total: 234.12 100.00

Electrolyte no. 1-1 generated a cloudy mixture that was not filtered.

Electrolyte no. 1-2 was formulated with the same ingredients in the sameamounts, but this electrolyte was filtered before testing.

TABLE 3 Electrolyte no. 1-3 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 34.82 Water 95 38.92 KBr 21 8.60 KCl 20 8.19 Acetic acid 1.110.45 1-ethyl-2-methylpyridinium bromide 4.96 2.03 tetraethylammoniumbromide 6.1 2.50 18-crown-6 0.55 0.23 cetyltrimethylammonium bromide 0.40.16 Citric acid 10 4.10 Total: 244.12 100.00

TABLE 4 Electrolyte no. 1-4 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 35.63 water 95 39.82 KBr 21 8.80 KCl 20 8.38 Acetic acid 1.110.47 1-ethyl-2-methylpyridinium bromide 4.96 2.08 tetraethylammoniumbromide 6.1 2.56 DME-PEG 2000 4 1.68 DME-PEG 2000 1 0.42cetyltrimethylammonium bromide 0.4 0.17 Total: 238.57 100.00

Test electrolyte formulation no. 3 was prepared as a filtered andunfiltered mixture.

TABLE 5 Electrolyte no. 1-5 formulation. Ingredient Amount (g) Wt %ZnBr₂ 101.3 36.78 water 100 36.31 KBr 23.8 8.64 KCl 37.2 13.51 Aceticacid 1.11 0.40 1-ethyl-2-methylpyridinium bromide 4.96 1.80tetraethylammonium bromide 6.1 2.21 18-crown-6 0.55 0.20cetyltrimethylammonium bromide 0.4 0.15 Total: 275.42 100

TABLE 6 Electrolyte no. 1-6 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 36.31 water 95 40.58 KBr 21 8.97 KCl 20 8.54 Acetic acid 1.110.47 1-butyl-1-methylpyridinium bromide 4.96 2.12trimethlypropylammonium bromide 6.1 2.61 18-crown-6 0.55 0.23cetyltrimethylammonium bromide 0.4 0.17 Total: 234.12 100.00

TABLE 7 Electrolyte no. 1-7 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 34.88 water 95 38.98 KBr 21 8.62 KCl 20 8.21 Acetic acid 1.110.46 1-butyl-1-methylpyridinium bromide 4.96 2.04trimethylpropylammonium bromide 6.1 2.50 18-crown-6 0.55 0.23 Potassiumdihydrogen citrate 10 4.10 Total: 243.72 100.00

TABLE 8 Electrolyte no. 1-8 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 36.37 water 95 40.65 KBr 21 8.99 KCl 20 8.56 Acetic acid 1.110.47 1-ethyl-2-methylpyridinium bromide 4.96 2.12 tetraethylammoniumbromide 6.1 2.61 18-crown-6 0.55 0.24 Total: 234.12 100.00

TABLE 9 Electrolyte no. 1-9 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 36.25 water 95 40.52 KBr 21 8.96 KCl 20 8.53 Acetic acid 1.110.47 1-ethyl-2-methylpyridinium bromide 4.96 2.12 tetraethylammoniumbromide 6.1 2.60 18-crown-6 1.1 0.47 cetyltrimethylammonium bromide 0.20.09 Total: 234.47 100.00

TABLE 10 Electrolyte no. 1-10 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 34.70 water 95 38.78 KBr 21 8.57 KCl 20 8.16 Acetic acid 1.110.45 1-ethyl-2-methylpyridinium bromide 9.92 4.05 tetraethylammoniumbromide 12.2 4.98 18-crown-6 0.55 0.22 cetyltrimethylammonium bromide0.2 0.08 Total: 244.98 100.00

TABLE 11 Electrolyte no. 1-11 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 34.85 water 95 38.95 KBr 21 8.61 KCl 20 8.20 Acetic acid 1.110.46 1-ethyl-2-methylpyridinium bromide 4.96 2.03 tetraethylammoniumbromide 6.1 2.50 18-crown-6 0.55 0.23 cetyltrimethylammonium bromide 0.20.08 Potassium dihydrogen citrate 10 4.10 Total: 243.92 100.00

TABLE 12 Electrolyte no. 1-12 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 36.34 Water 95 40.61 KBr 21 8.98 KCl 20 8.55 Acetic acid 1.110.47 1-butyl-3-methylpyridinium bromide 4.96 2.12 tetraethylammoniumbromide 6.1 2.61 18-crown-6 0.55 0.24 cetyltrimethylammonium bromide 0.20.09 Total: 233.92 100.00

TABLE 13 Electrolyte no. 1-13 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 36.34 Water 95 40.61 KBr 21 8.98 KCl 20 8.55 Acetic acid 1.110.47 1-ethyl-1-methylmorpholinium bromide 4.96 2.12 tetraethylammoniumbromide 6.1 2.61 18-crown-6 0.55 0.24 cetyltrimethylammonium bromide 0.20.09 Total: 233.92 100.00

TABLE 14 Electrolyte no. 1-14 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 36.34 Water 95 40.61 KBr 21 8.98 KCl 20 8.55 Acetic acid 1.110.47 1-ethyl-2-methylpyridinium bromide 4.96 2.12trimethylpropylammonium bromide 6.1 2.61 18-crown-6 0.55 0.24cetyltrimethylammonium bromide 0.2 0.09 Total: 233.92 100.00

TABLE 15 Electrolyte no. 1-15 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 35.29 Water 95 39.44 KBr 21 8.72 KCl 20 8.30 Acetic acid 1.110.46 1-butyl-3-methylpyridinium bromide 4.96 2.06trimethylpropylammonium bromide 6.1 2.53 18-crown-6 1.1 0.46cetyltrimethylammonium bromide 0.2 0.08 tetraethylammonium bromide 6.12.53 15-crown-5 0.29 0.12 Total: 240.86 100.00

TABLE 16 Electrolyte no. 1-16 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 34.69 Water 95 38.77 KBr 21 8.57 KCl 20 8.16 Acetic acid 1.110.45 1-ethyl-2-methylpyridinium bromide 9.92 4.05 tetraethylammoniumbromide 12.2 4.98 18-crown-6 0.55 0.22 cetyltrimethylammonium bromide0.2 0.08 SnCl₂•2H₂O ~0.0047 ~0.0019 In (In in nitric acid soln.) ~0.0025~0.0010 nitric acid (from soln.) ~0.026 ~0.0106 Total: ~240.86 ~100.00

TABLE 17 Electrolyte no. 1-17 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 34.07 Water 95 38.08 KBr 21 8.42 KCl 20 8.02 Acetic acid 1.110.45 1-ethyl-2-methylpyridinium bromide 9.92 3.98 tetraethylammoniumbromide 12.2 4.89 DME-PEG 2000 4 1.60 DME-PEG 1000 1 0.40cetyltrimethylammonium bromide 0.2 0.08 SnCl₂•2H₂O ~0.0047 ~0.0019 In(In in nitric acid soln.) ~0.0025 ~0.0010 nitric acid (from soln.)~0.026 ~0.0104 Total: ~249.46 ~100.00

TABLE 18 Electrolyte no. 1-18 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 34.00 Water 95 38.00 KBr 21 8.40 KCl 20 8.00 Acetic acid 1.110.44 1-ethyl-2-methylpyridinium bromide 9.92 3.97 tetraethylammoniumbromide 12.2 4.88 18-crown-6 0.55 0.22 DME-PEG 2000 4 1.60 DME-PEG 10001 0.40 cetyltrimethylammonium bromide 0.2 0.08 SnCl₂•2H₂O ~0.0047~0.0019 In (In in nitric acid soln.) ~0.0025 ~0.0010 nitric acid (fromsoln.) ~0.026 ~0.0104 Total: ~250.01 ~100.00

TABLE 19 Electrolyte no. 1-19 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 34.83 Water 95 38.93 KBr 5.3 2.17 KCl 29.8 12.21 Acetic acid1.11 0.45 1-ethyl-2-methylpyridinium bromide 9.92 4.07tetraethylammonium bromide 12.2 5.00 18-crown-6 0.55 0.23 DME-PEG 2000 41.64 DME-PEG 1000 1 0.41 cetyltrimethylammonium bromide 0.1 0.04SnCl₂•2H₂O ~0.0047 ~0.0019 In (In in nitric acid soln.) ~0.0025 ~0.0010nitric acid (from soln.) ~0.026 ~0.0107 Total: ~244.01 ~100.00

TABLE 20 Electrolyte no. 1-20 formulation. Ingredient Amount (g) Wt %ZnBr₂ 77.3 32.33 Water 95 39.73 ZnCl₂ 4.68 1.96 KCl 33.2 13.89 Aceticacid 1.11 0.46 1-ethyl-2-methylpyridinium bromide 9.92 4.15tetraethylammonium bromide 12.2 5.10 18-crown-6 0.55 0.23 DME-PEG 2000 41.67 DME-PEG 1000 1 0.42 cetyltrimethylammonium bromide 0.1 0.04SnCl₂•2H₂O ~0.0047 ~0.0020 In (In in nitric acid soln.) ~0.0025 ~0.0010nitric acid (from soln.) ~0.026 ~0.0109 Total: ~239.09 ~100.00

TABLE 21 Electrolyte no. 1-21 formulation. Ingredient Amount (g) Wt %ZnBr₂ 67.5 28.70 Water 95 40.39 ZnCl₂ 10.6 4.51 KCl 33.2 14.12 Aceticacid 1.11 0.47 1-ethyl-2-methylpyridinium bromide 9.92 4.22tetraethylammonium bromide 12.2 5.19 18-crown-6 0.55 0.23 DME-PEG 2000 41.70 DME-PEG 1000 1 0.43 cetyltrimethylammonium bromide 0.1 0.04SnCl₂•2H₂O ~0.0047 ~0.0020 In (In in nitric acid soln.) ~0.0025 ~0.0011nitric acid (from soln.) ~0.026 ~0.0111 Total: ~235.21 ~100.00

TABLE 22 Electrolyte no. 1-22 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 30.83 Water 95 34.46 KBr 21 7.62 KCl 45.8 16.61 Acetic acid1.11 0.40 1-ethyl-2-methylpyridinium bromide 9.92 3.60tetraethylammonium bromide 12.2 4.42 18-crown-6 0.55 0.20 DME-PEG 2000 41.45 DME-PEG 1000 1 0.36 cetyltrimethylammonium bromide 0.1 0.04SnCl₂•2H₂O ~0.0047 ~0.0017 In (In in nitric acid soln.) ~0.0025 ~0.0009nitric acid (from soln.) ~0.026 ~0.0094 Total: ~275.71 ~100.00

TABLE 23 Electrolyte no. 1-23 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 32.92 Water 95 36.80 KBr 21 8.13 KCl 20 7.75 Acetic acid 1.110.43 1-ethyl-2-methylpyridinium bromide 14.88 5.77 tetraethylammoniumbromide 18.3 7.09 18-crown-6 2.75 1.07 cetyltrimethylammonium bromide0.1 0.04 SnCl₂•2H₂O ~0.0047 ~0.0018 In (In in nitric acid soln.) ~0.0025~0.0010 nitric acid (from soln.) ~0.026 ~0.0101 Total: ~258.17 ~100.00

TABLE 24 Electrolyte no. 1-24 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 34.40 Water 95 38.44 KBr 21 8.50 KCl 20 8.09 Acetic acid 1.110.45 1-ethyl-2-methylpyridinium bromide 11.92 4.82 tetraethylammoniumbromide 10.2 4.13 18-crown-6 2.75 1.11 cetyltrimethylammonium bromide0.1 0.04 SnCl₂•2H₂O ~0.0047 ~0.0019 In (In in nitric acid soln.) ~0.0025~0.0010 nitric acid (from soln.) ~0.026 ~0.0105 Total: ~247.11 ~100.00

TABLE 25 Electrolyte no. 1-25 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 34.40 Water 95 38.44 KBr 21 8.50 KCl 20 8.09 Acetic acid 1.110.45 1-ethyl-2-methylpyridinium bromide 7.92 3.21 tetraethylammoniumbromide 14.2 5.75 18-crown-6 2.75 1.11 cetyltrimethylammonium bromide0.1 0.04 SnCl₂•2H₂O ~0.0047 ~0.0019 In (In in nitric acid soln.) ~0.0025~0.0010 nitric acid (from soln.) ~0.026 ~0.0105 Total: ~247.11 ~100.00

TABLE 26 Electrolyte no. 1-26 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 34.40 Water 95 38.44 KBr 21 8.50 KCl 20 8.09 Acetic acid 1.110.45 1-ethyl-2-methylpyridinium bromide 9.92 4.01 tetraethylammoniumbromide 12.2 4.94 18-crown-6 2.75 1.11 cetyltrimethylammonium bromide0.1 0.04 SnCl₂•2H₂O ~0.0047 ~0.0019 In (In in nitric acid soln.) ~0.0025~0.0010 nitric acid (from soln.) ~0.026 ~0.0105 Total: ~247.11 ~100.00

TABLE 27 Electrolyte no. 1-27 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 34.71 Water 95 38.79 KBr 21 8.57 KCl 20 8.17 Acetic acid 1.110.45 1-ethyl-2-methylpyridinium bromide 9.92 4.05 triethylmethylammoniumbromide 12.2 4.98 18-crown-6 0.55 0.22 cetyltrimethylammonium bromide0.1 0.04 SnCl₂•2H₂O ~0.0047 ~0.0019 In (In in nitric acid soln.) ~0.0025~0.0010 nitric acid (from soln.) ~0.026 ~0.0106 Total: ~244.91 ~100.00

TABLE 28 Electrolyte no. 1-28 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 36.37 Water 95 40.65 KBr 21 8.99 KCl 20 8.56 Acetic acid 1.110.47 1-ethyl-2-methylpyridinium bromide 9.92 4.24 tetraethylphosphoniumbromide 1 0.43 18-crown-6 0.55 0.24 cetyltrimethylammonium bromide 0.10.04 SnCl₂•2H₂O ~0.0047 ~0.0020 In (In in nitric acid soln.) ~0.0025~0.0011 nitric acid (from soln.) ~0.026 ~0.0111 Total: ~233.71 ~100.00

TABLE 29 Electrolyte no. 1-29 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 34.79 Water 95 38.89 KBr 21 8.60 KCl 20 8.19 Proprionic acid0.5 0.20 1-ethyl-2-methylpyridinium bromide 9.92 4.06tetraethylphosphonium bromide 12.2 4.99 18-crown-6 0.55 0.23cetyltrimethylammonium bromide 0.1 0.04 SnCl₂•2H₂O ~0.0047 ~0.0019 In(In in nitric acid soln.) ~0.0025 ~0.0010 nitric acid (from soln.)~0.026 ~0.0106 Total: ~244.30 ~100.00

TABLE 30 Electrolyte no. 1-30 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 34.68 Water 95 38.76 KBr 21 8.57 KCl 20 8.16 Zn acetate 1.320.54 1-ethyl-2-methylpyridinium bromide 9.92 4.05 tetraethylphosphoniumbromide 12.2 4.98 18-crown-6 0.55 0.22 cetyltrimethylammonium bromide0.1 0.04 SnCl₂•2H₂O ~0.0047 ~0.0019 In (In in nitric acid soln.) ~0.0025~0.0010 nitric acid (from soln.) ~0.026 ~0.0106 Total: ~245.12 ~100.00

TABLE 31 Electrolyte no. 1-31 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 34.71 Water 95 38.79 KBr 21 8.57 KCl 20 8.17 Acetic acid 1.110.45 1-ethyl-4-methylpyridinium bromide 9.92 4.05 tetraethylphosphoniumbromide 12.2 4.98 18-crown-6 0.55 0.22 cetyltrimethylammonium bromide0.1 0.04 SnCl₂•2H₂O ~0.0047 ~0.0019 In (In in nitric acid soln.) ~0.0025~0.0010 nitric acid (from soln.) ~0.026 ~0.0106 Total: ~244.91 ~100.00

In this Example 1, electrolytes containing various quaternary ammoniumagents of the invention were tested to evaluate the effect of thequaternary ammonium agents on the power and stability of a zinc bromideelectrochemical cell. FIG. 32 illustrates typical ranges for power andstability observed for most of the quaternary ammonium agents that weretested and classified as ammonium complexing agents, pyridinium orpyrrolidinium complexing agents, or imidazolium complexing agents.Stable electrolytes, i.e., electrolytes exhibiting a small change in pHafter exposure to Br₂ at 60° C. for seven days are desirable.Electrolytes with faster Br₂ kinetics, i.e., having a greater max powerat Tafel limiting current for Br reduction will result in cells withhigher power and are also desirable.

pH Stability Experiment

In this Example 1, stability experiments were performed on each of theelectrolytes above to determine whether the ingredients in electrolyteformulations were stable or experienced a significant change in pH whenexposed to Br₂ at 60° C. for seven days.

In the formulations above, the ZnBr₂, deionized water (di water), KBr,and KCl were added to a 500 mL flask and stirred until all saltsdissolved (about 30 min). Acetic acid was then added followed by ˜5 minof stirring, followed by the addition of a crown ether (when present),DME-PEG (when present) and any other organic ingredients. The quaternaryammonium agents were then added, followed by tin chloride dihydrate(when present) and the Indium-nitric acid solution (when present) weremixed into the formulation. Lastly, conc. HBr acid was added to each ofthe formulations above to adjust the pH to be about 3.

200 grams of electrolyte was placed in an amber bottle. Amber bottleswere used in order to keep the light away from light-sensitive bromine.The pH of the electrolyte was measured. 3.75 grams of bromine was addedto the electrolyte and the resulting mixture was carefully shaken for atleast twenty seconds.

The pH of the bomine-spiked electrolyte was then taken after the bottlewas shaken. Next, a piece of Parafilm was wrapped around the top/lid ofthe amber bottle to make it air tight, and the spiked electrolyte wasplaced in an oven at 60° C. for 7 days. After the 7 day period, the pHof the spiked electrolyte was measured (after cooling to roomtemperature) to evaluate the effect of bromine on the ingredients of theelectrolyte. After the pH of the one week old solution is measured andnoted, it has to be rewrapped with Parafilm and must be placed in theoven again. An electrolyte formulation is characterized as stable if itsinitial pH does not change by more than a value of ˜1.0 after beingspiked with bromine and subjected to the elevated temperature for the 7day period.

Power Experiment

Each of the bromine spiked electrolytes was added to a 3-neck roundbottom flask. A glassy carbon working electrode was added to the firstneck of the flask, a Zn metal counter electrode was added to the secondneck of the flask, and a saturated calomel reference electrode was addedto the third neck of the flask. All electrodes were submersed in thespiked electrolyte in the flask. A linear sweep voltammetry (LSV)experiment was performed where the potential was swept from 1.3V to 0.4Vvs. saturated calomel electrode. The voltage was swept at a rate of 1mV/s. The resulting current for Br oxidation and Br₂ reduction wasmeasured as a function of voltage.

The max power achieved during Br₂ reduction was calculated bymultiplying the limiting current for Br₂ reduction by the highestvoltage achieved at the limiting current. The max power for Br₂reduction was usually achieved around 0.4V vs. saturated calomelelectrode.

The results of the stability experiments and power experiments areprovided in FIGS. 32-34.

Example 1B—Electrochemical Cells Including Electrolyte Formulations ofExample 1A

Referring to FIGS. 35-38, selected electrolytes, formulated as describedin Example 1A, above, were added to dry electrochemical test cells thatwere evaluated for discharge capacity, Coulombic efficiency, Run Time,and energy efficiency as a function of charge cycle no. The dry cellsused in this example were formed as illustrated in FIG. 1. Each of thetest cells included a Calgon Carbon Zorflex ACC FM-10 carbon clothseparator that was cut into rectangles (width ˜5.31 cm, length ˜12.076cm) using a steel ruled die coated in ZrN of the same shape. The carbonmaterial was formulated with 20 kg of PTFE dispersion (60 wt %) (DuPontDISP30 PTFE dispersion), 10 kg Cabot PBX52 carbon blacks, 1 kg carbonfibers (3 mm), 10 kg Akzo-Nobel Ketjenblack EC600JD carbon blacks and 10kg of de-ionized water. The dry ingredients were premixed in a 55 gallondrum with an anti-static drum liner to form a relatively homogeneousmixture to which the PTFE dispersion and de-ionized water were added,and the resulting mixture was stirred to generate a dough material. Thedough material was formed from into blocks (length ˜5.24 cm, width ˜3.94cm, thickness ˜3.7 mm) and furnace dried to remove moisture to form thecarbon material blocks. Three of these blocks were added to the cathodecage in the test cell. The electrode plate and terminal plate wereformed of titanium metal that was coated with TiC (commerciallyavailable from Titanium Metals Corporation, Exton, Pa.) and formed intoplates having 45° chamfered corners (length ˜13.5 cm, width ˜8.375 cm,thickness ˜0.005 cm). The cathode cage was stamped to have a reducedsurface region of the pocket portion (length ˜5.187 cm, width ˜11.952cm), and the width of the cathode cage from the peripheral edge of oneflange to the peripheral edge of an opposing flange gave a total lengthof ˜5.73 cm and a total width of ˜12.495 cm, and a pocket depth of˜0.157 cm. A modulated hole pattern was chemically etched with acid intothe reduced surface region of the pocket portion of the cathode cagewherein the center of the adjacent holes along a row were spaced byabout 0.065 cm in the x-direction and every other row is spaced by about0.152 cm in the y-direction. The cathode cage was loaded with theseparator and 3 blocks of carbon material to form a cathode assemblythat was laser welded on the electrode plate with an offset of ˜0.694 cmfrom the bottom edge of the electrode plate and an offset of ˜0.502 cmfrom each of the side edges of the electrode plate. The cathode assemblywas laser welded to the electrode plate along the flange of the cathodecage. On a surface of the bipolar electrode plate opposite the cathodeassembly, a conductive cup-shaped member was laser welded such that thecenter of the cup-shaped member was approximately aligned or centeredwith the center of the reduced surface of the cathode cage. Thus, thiscomponent served as a terminal cathode assembly and bipolar electrodefor the test cell. The terminal anode assembly was likewise formed of aterminal endplate having dimensions substantially the same as those ofthe bipolar electrode plate with an elliptical cup-shaped member thatwas laser welded to the outer surface of the terminal anode endplatessuch that the center of the cup-shaped member was approximatelycollinear with the center of the cup-shaped member of the terminalcathode assembly. Conductive cup-shaped members were formed from stampedtitanium carbide material. The test cell was finally assembled with theinterposition of a single high density polyethylene frame member havinga sealing ring seated therein between the terminal anode assembly andthe terminal cathode assembly and compressing the components between twoopposing 6061-T6 aluminum compression plates. Dry test cells wereconstructed and loaded to capacity with the selected electrolytesdescribed above. For these experiments, control electrolyte no. 1, asdescribed in Example 2, was used in the control electrochemical cell.

During cell cycling, the cells were charged to a capacity of 750 mAh anddischarged at 20 mA/cm². The results of this testing is provided inFIGS. 35-38.

Example 2—Electrolyte No. 2-1

Bipolar Static (Non-Flowing) Cell Testing:

The following electrolyte formulations were tested in battery stacks,illustrated in FIGS. 18-20.

Each of the 28 bipolar electrodes of the battery stacks included aCalgon Carbon Zorflex ACC FM-10 carbon cloth separator that was cut intorectangles (width˜5.31 cm, length˜12.076 cm) using a steel ruled diecoated in ZrN of the same shape. The carbon material was formulated with20 kg of PTFE dispersion (60 wt %) (DuPont DISP30 PTFE dispersion), 10kg Cabot PBX52 carbon blacks, 1 kg carbon fibers (3 mm), 10 kgAkzo-Nobel Ketjenblack EC600JD carbon blacks and 10 kg of de-ionizedwater. The dry ingredients were premixed in a 55 gallon drum with ananti-static drum liner to form a relatively homogeneous mixture to whichthe PTFE dispersion and de-ionized water were added, and the resultingmixture was stirred to generate a dough material. The dough material wasformed from into blocks (length ˜5.24 cm, width ˜3.94 cm, thickness ˜3.7mm) and furnace dried to remove moisture to form the carbon materialblocks. Three of these blocks were added to the cathode cage in the testcell. The bipolar electrode plate was formed of titanium metal that wascoated with TiC (commercially available from Titanium MetalsCorporation, Exton, Pa.) and formed into plates having 45° chamferedcorners (length ˜13.5 cm, width ˜8.375 cm, thickness ˜0.005 cm). Thecathode cage was stamped to have a reduced surface region of the pocketportion (length ˜5.187 cm, width ˜11.952 cm), and the width of thecathode cage from the peripheral edge of one flange to the peripheraledge of an opposing flange gave a total length of ˜5.73 cm and a totalwidth of ˜12.495 cm, and a pocket depth of ˜0.157 cm. A modulated holepattern was chemically etched with acid into the reduced surface regionof the pocket portion of the cathode cage wherein the center of theadjacent holes along a row were spaced by about 0.065 cm in thex-direction and every other row is spaced by about 0.152 cm in they-direction. The cathode cage was loaded with the separator and 3 blocksof carbon material to form a cathode assembly that was laser welded onthe electrode plate with an offset of ˜0.694 cm from the bottom edge ofthe electrode plate and an offset of ˜0.502 cm from each of the sideedges of the electrode plate. The cathode assembly was laser welded tothe electrode plate along the flange of the cathode cage.

The terminal cathode assembly was formed by laser welding a conductivecup-shaped member on a bipolar electrode, as described above, on theside opposite the cathode assembly, such that the center of thecup-shaped member was approximately aligned or centered with the centerof the reduced surface of the cathode assembly. The terminal anodeassembly was likewise formed of a terminal endplate having dimensionssubstantially the same as those of the bipolar electrode plate with anelliptical cup-shaped member that was laser welded to the outer surfaceof the terminal anode endplate such that the center of the cup-shapedmember was approximately collinear with the center of the cup-shapedmember of the terminal cathode assembly. Conductive cup-shaped memberswere formed from stamped titanium carbide material. A portion of theinner surface of the terminal anode endplate corresponding with thereduced surface of the opposing cathode assembly of the terminal cathodeassembly was sandblasted to provide a rough surface. The test batterystacks were assembled with the interposition of a high densitypolyethylene frame member between 1) the cathode terminal endplate and abipolar electrode, 2.) each of the bipolar electrodes, and 3), theterminal anode endplate and a bipolar electrode, requiring a total of 30frame members. Each of the 30 frame members had a sealing ring seated onits first surface and a sealing ring seated on its second surface. Twoopposing 6061-T6 aluminum compression plates compressed the 30 framemembers against adjacent components using tie rods and fasteners asillustrated in FIGS. 18-20. The dry battery stacks were constructed andloaded to capacity with the electrolytes described below.

Control Electrolyte No. 1:

The formulation for control electrolyte no. 1 was based on a formuladescribed in U.S. Pat. No. 4,482,614. Control electrolyte no. 1 wasformulated as follows:

TABLE 32 Formulation for control electrolyte no. 1. Ingredient Amount Wt% ZnBr₂ 675 g 67.5 NH₄Cl 100 g 10 PEG  15 g 1.5 di water 210 g 21 Total:1000 g  100

Control Electrolyte No. 2:

The formulation for control electrolyte no. 2 was based on a formuladescribed in Yan, Jung Hoon, Yan, Hyeon Sun, Ra, Ho Won, et al. Effectof a surface active agent on performance of zing/bromine redox flowbatteries: Improvement in current efficiency and system stability,Journal of Power Sources 275 (2015) 294-297. Control electrolyte no. 2was formulated as follows:

TABLE 33 Formulation for control electrolyte no. 2. Ingredient Amount Wt% ZnBr₂ 507 g 50.7 ZnCl₂  68 g 6.8 N-methly-N-ethyl pyrrolidiniumbromide 155 g 15.5 di water 270 g 27 Total: 1000 g  100

Electrolyte Formulation 2-1:

An electrolyte of the present invention was formulated as follows:

TABLE 34 Test electrolyte no. 2-1 formulation. Ingredient Amount ZnBr₂345 g KBr 85.2 g KCl 81.2 g tetraglyme 32.5 g DME-PEG 2000 16.2 gtetraethylammonium bromide 25.5 g MEMBr 8.5 g neopentyl glycol 16.2 gtert-butyl alcohol 4.1 g di water 385 g SnCl₂•2H₂O 10 ppm In 10 ppm

The pH for this electrolyte was adjusted to 3 with conc. HBr.

For these tests, each electrolyte was loaded into two test stacks toprovide duplicate test data (i.e., n=2). Each of the test stacks wasinitially charged with a constant voltage of 38.0 V, terminating at 15min or less than 100 mA. Charging continued at +7.16 Amps constantcurrent, terminating at 58.5 V or 30 Ah total accumulated charge. Thecells were discharged at ˜8.0 A constant current, terminating at 33 V.

Results:

Referring to FIGS. 28, 29A, and 29B, the plot of battery stack energy(Wh) as a function of charge cycle number demonstrates that the teststacks using the test electrolyte maintained greater charge anddischarge energies over more charge cycles than either of the controlelectrolytes. And, the plot of battery capacity (Ah) as a function ofcharge cycle number demonstrates that the test stacks using theelectrolyte 2-1 formulation maintained greater charge capacities overmore charge cycles than either of the control electrolytes.

Example 3: Cathode Cage Hole Pattern

Negative Control—Two dry test cells were formed as described in Example1B, except the cathode cage in these two cells possessed an un-modulatedseries of holes on the pocket portion of the cathode cage. The dry testcells were loaded to capacity with control electrolyte no. 1 andcharged.

Test Cells—Three dry test cells were formed as described in Example 1B,including the modulated hole pattern on the reduced surface of thepocket portion of the cathode cage. The dry test cells were loaded tocapacity with control electrolyte no. 1 and charged.

Referring to FIGS. 30A-31C, after charging, the test cells weredeconstructed and zinc plating on the anodic surfaces of the cells wereevaluated. FIGS. 30A and 30B show zinc plating in the negative controltest cells while FIGS. 31A-31C show zinc plating on the test cells.FIGS. 30A-31C illustrate the enhanced zinc plating that was observed forthe test cells formed from cathode cages having modulated hole patternson their respective pocket regions. As shown in FIGS. 30A and 30B, thezinc metal deposits in an irregular pattern when the correspondingcathode cage has an un-modulated series of holes. In contrast, and asshown in FIGS. 31A, 31B, and 31C, the zinc metal deposits in a moreregular and complete pattern when the corresponding cathode cage has amodulated series of holes.

Example 4: Battery Stack Performance

Referring to FIGS. 24, 25A, 25B, 26, 27A, and 27B, test stacks, asdescribed in Example 1, underwent charge/discharge cycling to evaluatethe performance properties of the test stacks. The data from thistesting is plotted in the figures referenced in this Example 3.

Example 5: Alkyl Ammonium Bromides in Electrolytes

The following electrolytes were formulated as follows:

TABLE 35 Electrolyte no. 5-1 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 34.71 Water 95 38.79 KBr 21 8.57 KCl 20 8.17 Acetic acid 1.110.45 1-ethyl-2-methylpyridinium bromide 9.92 4.05 chloroethylammoniumchloride 12.2 4.98 18-crown-6 0.55 0.22 cetyltrimethylammonium bromide0.1 0.04 SnCl₂•2H₂O ~0.0047 ~0.0019 In (In in nitric acid soln.) ~0.0025~0.0010 nitric acid (from soln.) ~0.026 ~0.0106 Total: ~244.91 ~100.00

TABLE 36 Electrolyte no. 5-2 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 34.73 Water 95 38.82 KBr 21 8.58 KCl 20 8.17 Acetic acid 1.110.45 1-ethyl-4-methylpyridinium bromide 9.92 4.05 tetraethylammoniumbromide 6.0 2.45 trimethylproplyammonium bromide 6.0 2.45 18-crown-60.55 0.22 cetyltrimethylammonium bromide 0.1 0.04 SnCl₂•2H₂O ~0.0047~0.0019 In (In in nitric acid soln.) ~0.0025 ~0.0010 nitric acid (fromsoln.) ~0.026 ~0.0106 Total: ~244.71 ~100.00

TABLE 37 Electrolyte no. 5-3 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 34.73 Water 95 38.82 KBr 21 8.58 KCl 20 8.17 Acetic acid 1.110.45 1-ethyl-4-methylpyridinium bromide 9.92 4.05 tetraethylammoniumbromide 6.0 2.45 triethylmethylammonium bromide 6.0 2.45 18-crown-6 0.550.22 cetyltrimethylammonium bromide 0.1 0.04 SnCl₂•2H₂O ~0.0047 ~0.0019In (In in nitric acid soln.) ~0.0025 ~0.0010 nitric acid (from soln.)~0.026 ~0.0106 Total: ~244.71 ~100.00

TABLE 38 Electrolyte no. 5-4 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 34.73 Water 95 38.82 KBr 21 8.58 KCl 20 8.17 Acetic acid 1.110.45 1-ethyl-4-methylpyridinium bromide 9.92 4.05 tetraethylammoniumbromide 6.0 2.45 hexyltrimethylammonium bromide 6.0 2.45 18-crown-6 0.550.22 cetyltrimethylammonium bromide 0.1 0.04 SnCl₂•2H₂O ~0.0047 ~0.0019In (In in nitric acid soln.) ~0.0025 ~0.0010 nitric acid (from soln.)~0.026 ~0.0106 Total: ~244.71 ~100.00

TABLE 39 Electrolyte no. 5-5 formulation. Ingredient Amount (g) Wt %ZnBr₂ 85 34.73 Water 95 38.82 KBr 21 8.58 KCl 20 8.17 Acetic acid 1.110.45 1-ethyl-4-methylpyridinium bromide 9.92 4.05 tetraethylammoniumbromide 6.0 2.45 triethyl-N-methoxymethylammonium bromide 6.0 2.4518-crown-6 0.55 0.22 cetyltrimethylammonium bromide 0.1 0.04 SnCl₂•2H₂O~0.0047 ~0.0019 In (In in nitric acid soln.) ~0.0025 ~0.0010 nitric acid(from soln.) ~0.026 ~0.0106 Total: ~244.71 ~100.00

Each of the solutions in this example was loaded into a dry batterystack, as described in Example 2.

Each of the test stacks was initially charged with a constant voltage of38.0 V, terminating at 15 min or less than 100 mA. Charging continued at+7.16 Amps constant current, terminating at 58.5 V or 30 Ah totalaccumulated charge. The cells were discharged at ˜8.0 A constantcurrent, terminating at 33 V.

A plot of the cyclic voltammetry for each of the test stacks is providedin FIG. 39.

Other Embodiments

It should be apparent that the foregoing relates only to the preferredembodiments of the present invention and that numerous changes andmodifications may be made herein without departing from the spirit andscope of the invention as defined by the following claims andequivalents thereof.

What is claimed is:
 1. An electrolyte for use in a secondary zincbromine electrochemical cell comprising: from about 25 wt % to about 70wt % of ZnBr₂; from about 5 wt % to about 50 wt % of water; and one ormore quaternary ammonium agents, wherein the electrolyte comprises fromabout 0.05 wt % to about 10 wt % of the one or more quaternary ammoniumagents.
 2. The electrolyte according to claim 1, further comprising:from about 1 wt % to about 15 wt % of KBr; from about 5 wt % to about 20wt % of KCl.
 3. The electrolyte according to claim 1 or claim 2,comprising from about 27 wt % to about 40 wt % of ZnBr₂.
 4. Theelectrolyte according to any one of claims 1-3, comprising from about 28wt % to about 37 wt % of ZnBr₂.
 5. The electrolyte according to any oneof claims 1-4, comprising from about 1.5 wt % to about 7.5 wt % ofZnCl₂.
 6. The electrolyte according to any one of claims 1-5, comprisingfrom about 30 wt % to about 45 wt % of water.
 7. The electrolyteaccording to any one of claims 1-6, comprising from about 35 wt % toabout 41 wt % of water.
 8. The electrolyte according to any one ofclaims 1-7, comprising from about 2 wt % to about 10 wt % of KBr.
 9. Theelectrolyte according to any one of claims 1-8, comprising from about7.3 wt % to about 9.2 wt % of KBr.
 10. The electrolyte according to anyone of claims 1-9, comprising from about 7 wt % to about 17 wt % of KCl.11. The electrolyte according to any one of claims 1-10, furthercomprising from about 0.5 wt % to about 10 wt % of a glyme.
 12. Theelectrolyte according to claim 11, wherein the glyme comprisesmonoglyme, diglyme, triglyme, tetraglyme, pentaglyme, hexaglyme, or anycombination thereof.
 13. The electrolyte according to claim 11 or claim12, wherein the glyme comprises tetraglyme.
 14. The electrolyteaccording to any one of claims 11-13, comprising from about 2 wt % toabout 4 wt % of tetraglyme.
 15. The electrolyte according to any one ofclaims 1-14, comprising from about 0.5 wt % to about 2.5 wt % of anether selected from DME-PEG, dimethyl ether, or any combination thereof.16. The electrolyte according to claim 15, wherein the electrolytecomprises DME-PEG, and the DME-PEG has an average molecular weight offrom about 350 amu to about 3000 amu.
 17. The electrolyte according toclaim 15 or claim 16, wherein the DME-PEG has an average molecularweight of from about 1200 amu to about 3000 amu.
 18. The electrolyteaccording to any one of claims 15-17, wherein the DME-PEG is DME-PEG2000, DME-PEG 1000, or a combination thereof.
 19. The electrolyteaccording to any one of claims 15-18, comprising from about 1 wt % toabout 2 wt % DME-PEG
 2000. 20. The electrolyte according to any one ofclaims 15-19, comprising from about 0.25 wt % to about 0.75 wt % DME-PEG1000.
 21. The electrolyte according to any one of claims 15-20,comprising from about 1 wt % to about 2 wt % DME-PEG 2000 and from about0.25 wt % to about 0.75 wt % DME-PEG
 1000. 22. The electrolyte accordingto any one of claims 1-21, further comprising from about 0.1 wt % toabout 1.0 wt % of an alcohol, wherein the alcohol is substantiallymiscible in water.
 23. The electrolyte according to claim 22, whereinthe alcohol comprises a C₁₋₄ alcohol.
 24. The electrolyte according toclaim 22 or claim 23, wherein the alcohol comprises methanol, ethanol,1-propanol, iso-propanol, 1-butanol, sec-butanol, iso-butanol,tert-butanol, or any combination thereof.
 25. The electrolyte accordingto any one of claims 22-24, comprising from about 0.25 wt % to about0.75 wt % of tert-butanol.
 26. The electrolyte according to any one ofclaims 1-25, further comprising from about 0.5 wt % to about 5 wt % of aC₁₋₁₀ glycol.
 27. The electrolyte according to claim 26, wherein theglycol comprises ethylene glycol, propylene glycol, 1,3-butylene glycol,1,4-butylene glycol, neopentyl glycol, hexalene glycol, or anycombination thereof.
 28. The electrolyte according to claim 26 or claim27, comprising from about 0.25 wt % to about 2.5 wt % of neopentylglycol.
 29. The electrolyte according to any one of claims 1-28, furthercomprising from about 0.05 wt % to about 20 wt % of one or morequaternary ammonium agents.
 30. The electrolyte according to claim 29,wherein the one or more quaternary ammonium agents comprises aquaternary ammonium agent selected from the group consisting of ammoniumchloride, tetraethylammonium bromide, trimethylpropylammonium bromide,N-methyl-N-ethylmorpholinium bromide, N-methyl-N-ethylmorpholiniumbromide (MEMBr), 1-ethyl-1-methylmorpholinium bromide,N-methyl-N-butylmorpholinium bromide, N-methyl-N-ethylpyrrolidiniumbromide, N,N,N-triethyl-N-propylammonium bromide,N-ethyl-N-propylpyrrolidinium bromide, N-propyl-N-butylpyrrolidiniumbromide, N-methyl-N-butylpyrrolidinium bromide,1-methyl-1-butylpyrrolidinium bromide,N-ethyl-N-(2-chloroethyl)pyrrolidinium bromide,N-methyl-N-hexylpyrrolidinium bromide, N-methyl-N-pentylpyrrolidiniumbromide, N-ethyl-N-pentylpyrrolidinium bromide,N-ethyl-N-butylpyrrolidinium bromide,trimethylene-bis(N-methylpyrrolidinium) dibromide,N-butyl-N-pentylpyrrolidinium bromide, N-methyl-N-propylpyrrolidiniumbromide, N-propyl-N-pentylpyrrolidinium bromide,1-ethyl-4-methylpyridinium bromide, 1-ethyl-2-methylpyridinium bromide,1-butyl-3-methylpyridinium bromide, cetyltrimethylammonium bromide, andany combination thereof.
 31. The electrolyte according to claim 30,wherein the one or more quaternary ammonium agents comprises aquaternary ammonium agent selected from the group consisting of ammoniumchloride, tetraethylammonium bromide, trimethylpropylammonium bromide,N-methyl-N-ethylmorpholinium bromide (MEMBr),1-ethyl-1-methylmorpholinium bromide, N-methyl-N-ethylpyrrolidiniumbromide, 1-methyl-1-butylpyrrolidinium bromide,1-ethyl-4-methylpyridinium bromide, 1-ethyl-2-methylpyridinium bromide,1-butyl-3-methylpyridinium bromide, cetyltrimethylammonium bromide, andany combination thereof.
 32. The electrolyte according to any one ofclaims 29-31, wherein the one or more quaternary ammonium agentscomprises about 3.5 wt % to about 4.5 wt % 1-ethyl-4-methylpyridiniumbromide.
 33. The electrolyte according to any one of claims 29-32,wherein the one or more quaternary ammonium agents comprises about 1 wt% to about 7 wt % 1-ethyl-2-methylpyridinium bromide.
 34. Theelectrolyte according to any one of claims 29-33, wherein the one ormore quaternary ammonium agents comprises about 1.5 wt % to about 2.5 wt% 1-methyl-1-butylpyrrolidinium bromide.
 35. The electrolyte accordingto any one of claims 29-34, wherein the one or more quaternary ammoniumagents comprises about 1.5 wt % to about 2.5 wt %1-butyl-3-methylpyridinium bromide.
 36. The electrolyte according to anyone of claims 29-35, wherein the one or more quaternary ammonium agentscomprises about 1.5 wt % to about 5 wt % 1-methyl-1-ethylmorpholiniumbromide.
 37. The electrolyte according to any one of claims 29-36,wherein the one or more quaternary ammonium agents comprises about 0.5wt % to about 1.5 wt % N-methyl-N-ethylmorpholinium bromide (MEMBr). 38.The electrolyte according to any one of claims 29-37, wherein the one ormore quaternary ammonium agents comprises about 14.5 wt % to about 16.5wt % N-methyl-N-ethylpyrrolidinium bromide.
 39. The electrolyteaccording to any one of claims 29-38, wherein the one or more quaternaryammonium agents comprises about 2 wt % to about 3 wt %trimethylpropylammonium bromide.
 40. The electrolyte according to anyone of claims 29-39, wherein the one or more quaternary ammonium agentscomprises about 2 wt % to about 8 wt % tetraethylammonium bromide. 41.The electrolyte according to any one of claims 29-40, wherein the one ormore quaternary ammonium agents comprises about 0.05 wt % to about 0.2wt % cetyltrimethylammonium bromide.
 42. The electrolyte according toany one of claims 1-41, further comprising less than 1 wt % of one ormore additives selected from Sn, In, Ga, Al, Tl, Bi, Pb, Sb, Ag, Mn, orFe.
 43. The electrolyte according to claim 42, wherein the one or moreadditives are selected from about 0.0008 wt % to about 0.0012 wt % ofSnCl₂.H₂O, from about 0.0008 wt % to about 0.0012 wt % of In, andcombinations thereof.
 44. The electrolyte according to any one of claims1-43, further comprising an acid, or the conjugate base of an acid,selected from acetic acid, nitric acid, and citric acid.
 45. Theelectrolyte according to claim 44, comprising from about 0.3 wt % toabout 0.6 wt % acetic acid.
 46. The electrolyte according to claim 44 orclaim 45, comprising from about 0.12 wt % to about 0.08 wt % nitricacid.
 47. The electrolyte according to any one of claims 44-46,comprising from about 3.5 wt % to about 4.5 wt % citric acid.
 48. Theelectrolyte according to any one of claims 44-47, comprising from about3.5 wt % to about 4.5 wt % potassium dihydrogen citrate.
 49. Theelectrolyte according to any one of claims 1-48, comprising from about0.05 wt % to about 0.75 wt % of a crown ether.
 50. The electrolyteaccording to claim 49, comprising from about 0.15 wt % to about 0.5 wt %of 18-crown-6.
 51. The electrolyte according to claim 49 or claim 50,comprising from about 0.05 wt % to about 0.2 wt % of 15-crown-5.
 52. Anelectrolyte for use in a secondary zinc halide electrochemical cellcomprising: from about 27 wt % to about 40 wt % of ZnBr₂ by weight ofthe electrolyte; from about 35 wt % to about 41 wt % of water; fromabout 7.3 wt % to about 9.2 wt % of KBr; from about 7 wt % to about 17wt % of KCl; from about 0.3 wt % to about 0.6 wt % acetic acid; and fromabout 2 wt % to about 8 wt % tetraethylammonium bromide.
 53. Theelectrolyte according to claim 52, further comprising from about 0.05 wt% to about 0.2 wt % of cetyltriethylammonium bromide (CTAB).
 54. Theelectrolyte according to claim 52 or claim 53, further comprising fromabout 3.5 wt % to about 4.5 wt % of citric acid monohydrate.
 55. Theelectrolyte according to any one of claims 52-54, further comprisingfrom about 3.5 wt % to about 4.5 wt % of potassium dihydrogen citratemonohydrate.
 56. An electrolyte for use in a secondary zinc halideelectrochemical cell comprising: from about 27 wt % to about 40 wt % ofZnBr₂ by weight of the electrolyte; from about 35 wt % to about 41 wt %of water; from about 7.3 wt % to about 9.2 wt % of KBr; from about 7 wt% to about 17 wt % of KCl; from about 0.15 wt % to about 0.5 wt % of18-crown-6; and from about 0.05 wt % to about 0.2 wt %cetyltrimethylammonium bromide.
 57. The electrolyte according to claim56, further comprising from about 2 wt % to about 8 wt %tetraethylammonium bromide.
 58. The electrolyte according to claim 56 orclaim 57, further comprising from about 0.3 wt % to about 0.6 wt %acetic acid.
 59. The electrolyte according to any one of claims 56-58,comprising from about 1 wt % to about 2 wt % DME-PEG
 2000. 60. Theelectrolyte according to any one of claims 56-59, comprising from about0.25 wt % to about 0.75 wt % DME-PEG
 1000. 61. The electrolyte accordingto any one of claims 56-60, comprising from about 1 wt % to about 2 wt %DME-PEG 2000 and from about 0.25 wt % to about 0.75 wt % DME-PEG 1000.62. A method of preparing an electrolyte for use in a secondary zinchalide electrochemical cell comprising: mixing ZnBr₂, KBr, KCl, and oneor more quaternary ammonium agents under aqueous conditions to generatea mixture and stirring the mixture until the solids have dissolved,wherein the mixture comprises: from about 27 wt % to about 40 wt % ofZnBr₂; from about 7.3 wt % to about 9.2 wt % of KBr; from about 7 wt %to about 17 wt % of KCl; from about 0.05 wt % to about 20 wt % of theone or more quaternary ammonium agents; and from about 35 wt % to about41 wt % of water.